IDLE AND OFF-IDLE OPERATION OF A TWO-STROKE FUEL-INJECTED MULTI-CYLINDER INTERNAL COMBUSTION ENGINE

Abstract: A multiple cylinder two-stroke fuel-injected internal combustion engine is operated at idle by interrupting the fuel injection stages in a predetermined pattern such that over a certain number of crankshaft revolutions a fewer number of injections occur than over the same number of revolutions at non-idle. The quantity of fuel injected per injection is increased relative to that required to operate the engine at idle without any injection interruptions. Spark timing is also advanced.

Description: IDLE AND OFF-IDLE•OPERATION OF A TWO-STROKE FUEL-INJECTED MULTI-CYLINDER INTERNAL COMBUSTION ENGINE BACKGROUND AND SUMMARY OF THE INVENTION When running at idle, an internal combustion engine is only lightly loaded and therefore ingests fuel at a rate that is small in comparison to rates that are required at higher speeds and loads. When fuel is introduced into the engine cylinders by means of an individual electronically controlled fuel injector for each cylinder, each injector is required to operate over a rather extensive range of opening and closing times. In order to operate the engine at high speeds and loads, it is vital that each injector have the ability to flow fuel at a certain flow rate; yet at idle, a much lower flow rate is used. Stated another way, such an injector is required to have a relatively large dynamic range. Where a particular injector is designed for a specific maximum flow rate, it may be difficult for such an injector to accurately inject fuel at the low end of the required range. This difficulty is amplified in a two-stroke engine. A further consideration related to a two-stroke engine involves the matter of scavenging. The inherent nature of the design of a two-stroke engine leaves a significant amount of residual combustion products in a combustion chamber as the chamber is being prepared for the immediately succeeding combustion event. The presence of such residual products influences the nature of the combustion process, and when a two-stroke engine is used as the powerplant of an automotive vehicle, factors such as fuel economy and exhaust emissions are affected. A known means of improving scavenge efficiency and increasing the quantity of fuel injected per cycle is to retard the spark timing. The present invention relates to means and methodology for improving the operation of a 5multi-cylinder fuel-injected two-stroke internal combustion engine at idle and off-idle. The invention involves the deliberate skipping of injection cycles in particular patterns which serve to create modest, but nonetheless meaningful, improvements in operating l oefficiency and exhaust emissions without causing any noticeable degradation in the quality of the engine's operation at idle. Briefly, the pattern is such that over a certain number of engine crankshaft revolutions the interruptions of fuel injection into each individual 15cylinder are caused to occur at non-consecutive two-stroke cycles and the interruptions in the sequence of injection from cylinder to cylinder are caused to occur non-consecutively. Each interrupted injection results in the introduction of air alone into the associated cylinder 2o°n the immediately succeeding cycle whereby the residual combustion products are diluted by the charge of air. The scavenging that occurs after the interrupted fuel injection cycle therefore results in a cylinder that is much better purged of combustion products before the next 2 5 combustion event that takes place in that cylinder. Accordingly, that combustion event will make more efficient use of the injected charge of fuel. Since the idle load that is imposed on the engine requires a certain power output from the engine, the 30 skipping of certain injection cycles at idle means that on the average each combustion event in each cylinder must produce a higher power output in comparison to the situation where injection cycles are not skipped. This higher power output is accomplished by causing each injector to flow a correspondingly higher amount of fuel when the injection skipping pattern is in effect at idle. Two benefits result from the invention. One, it means that the lower limit of the fuel injectors' dynamic ranges 5does not have to be as low as in the case of non-skipping, and two, it means that the spark timing can be advanced over the value used for non-skip operation. Reducing the dynamic range requirement of a fuel injector is an advantage for obvious reasons, and the advancement of lOspark timing of course promotes better combustion efficiency and fuel economy. The features of the invention that have been mentioned above, along with further ones, will be seen in the ensuing detailed description of a presently preferred 5embodiment of the invention. The description includes the best mode contemplated at the present time for the practice of the invention. As an aid to explaining the inventive principles, a drawing accompanies the disclosure. 0 BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a chart portraying a fuel injection pattern of operation for a six-cylinder, two-stroke engine. 5 Fig. 2 is a flow diagram of a micro-computer routine illustrating off-idle operation. Fig. 3 is a chart portraying another fuel injection pattern of operation for a six-cylinder, two-stroke engine. Q Fig. 4 is a chart portraying a fuel injection pattern of operation for a four-cylinder, two-stroke engine. Fig. 5 is a chart portraying another fuel injection pattern of operation for a four-cylinder, two-stroke engine. DESCRIPTION OF THE•PREFERRED EMBODIMENT Fig. 1 presents a fuel injection pattern for a six-cylinder, fuel-injected, two-stroke engine operating at idle. The order in which the cylinders are sequentially injected when the engine is running at non-idle is: cylinder #1, cylinder #2, cylinder #3, cylinder #4, cylinder #5, cylinder #6. This sequential pattern of injection is altered at engine idle by the 0selective skipping of injections according to the pattern portrayed. The letter I designates the occurrence of injection by operation of the corresponding injector, while the letter S denotes the skipping of an injection by the non-operation of the corresponding injector. Thus, in 5Fig. 1, the abscissa represents the engine cylinders, and the ordinate, the crankshaft revolutions. The sequence of Fig. 1 comprises the repeating pattern: skip, inject, inject, skip, inject. Hence, after the injection of cylinder #5 during crankshaft revolution o#l, the pattern repeats, beginning with the skipping of cylinder #6 during crankshaft revolution #1 and ending with the injection of cylinder #4 during crankshaft revolution #2. In similar fashion, occurrences of the pattern end with the injection of cylinder #3 during 5crankshaft revolution #3, with the injection of cylinder #2 during crankshaft revolution #4, with the injection of cylinder #1 during crankshaft revolution #5, and with the injection of cylinder #6 during crankshaft revolution #5. As subsequently appears, the pattern that occurs during -crankshaft revolution #6 is identical to that occurring during crankshaft revolution #1, the pattern that occurs during crankshaft revolution #7 is identical to that occurring during crankshaft revolution #2, and so forth. It is to be observed that over a certain number of engine crankshaft revolutions the interruptions in each individual cylinder are caused to occur at non-consecutive two-stroke cycles and the interruptions in the sequence of 5injection from cylinder to cylinder are caused to occur non-consecutively. In other words, as a function of time, there are never two consecutive interruptions, nor does any cylinder experience interruptions on consecutive crankshaft revolutions. The pattern produces an average 0 injector operating rate of 60% as compared with the 100% rate that occurs at non-idle. To maintain the power necessary to operate the engine at idle, the amount of fuel injected per injection is increased over that which would otherwise be required. In this way each injector is 5 not required to meter as low an amount of fuel as would otherwise be the case, and therefore can be more precise. Because each combustion event must deliver more power output than would otherwise be the case, spark timing can be advanced to improve combustion efficiency. Thus, Q definite advantages accrue by utilization of the invention. Because a skipped injection cycle would be noticeable at non-idle, deliberate skipping is permitted only at idle. Therefore, when the engine leaves idle, such 5 departure from idle must be detected and the fuel delivery to the individual injectors re-adjusted. Since the injectors are electronically controlled, typically by a digital micro-computer control, a suitable routine is embodied in the micro-computer, and an example of such a routine is presented in Fig. 2. Parameters indicative of departure from idle operation are monitored and use to revert the micro-computer control to non-idle operation. The illustrated routine monitors engine speed, throttle position, manifold absolute pressure, and airflow into the engine. Change in any one of these monitored parameters that is indicative of a change from idle to non-idle operation will revert the micro-computer to non-idle operation. From the standpoint of fuel injection, one of 5the importance consequences of such reversion is to remove the fuel flow adjustment factor that was instituted upon idle operation due to the reduced percentage of injector operations. There is of course a complementary routine that caused the fuel flow adjustment factor to be 0instituted upon detection of idle operation. Simultaneously, spark timing is adjusted. It is possible that an engine could be operated at idle with less than the 60% injector operation represented by Fig. 1. Fig. 3 represents a pattern that is the 5inverse of that of Fig. 1, and hence represents 40% injector operation. According to this pattern, over a certain number of engine crankshaft revolutions the injections in each individual cylinder are caused to occur at non-consecutive two-stroke cycles, and the injections oin the sequence of injections from cylinder to cylinder are caused to occur non-consecutively. In this mode of operation suitable adjustments in fuel flow factor, and spark timing, are made in analogous manner to those previously described in connection with operation 5according to Fig. 1. Fig. 4 discloses an injector operating pattern for the idle operation of a four-cylinder, two-stroke engine. The designation I identifies an injection while the designation S denotes a skip. The cylinder injection Q order is cylinder #1, cylinder #2, cylinder #3, and cylinder #4. The repeated sequence is inject, skip, inject, inject, skip so that the crankshaft must rotate five times before the sequence during a single revolution is the same again. The adjustments to fuel flow factor, and spark timing, .are made in analogous manner to those described for the six-cylinder engine. As in the embodiment of Fig. 1, over a certain number of engine crankshaft revolutions the interruptions in each 5individual cylinder are caused to occur at non-consecutive two-stroke cycles and the interruptions in the sequence of injection from cylinder to cylinder are caused to occur non-consecutively. In other words, as a function of time, there are never two consecutive interruptions, nor does 0any individual cylinder experience interruptions on consecutive crankshaft revolutions. Fig. 5 presents an operating pattern which is complementary to the pattern of Fig. 4. Over a certain number of engine crankshaft revolutions the injections in 5each individual cylinder are caused to occur at non-consecutive two-stroke cycles and the injections in the sequence of injection from cylinder to cylinder are caused to occur non-consecutively. As a result, there are never two consecutive injections, nor does any cylinder oexpedience injections on consecutive crankshaft revolutions. While a presently preferred embodiment of the invention has been disclosed, it must be appreciated that principles of the invention may be practiced in other 5equivalent embodiments.

Claims: WHAT IS CLAIMED IS: 1. In a multiple cylinder two-stroke fuel-injected internal combustion engine which operates at non-idle in a manner such that the fuel is injected into each cylinder during the fuel injection stage of consecutive two-stroke cycles of the cylinder, the method for operating the engine at idle which comprises interrupting the fuel injection stages of the cylinders from that which occurs at non-idle engine operation in such a pattern that over a certain number of engine crankshaft revolutions the interruptions in each individual cylinder are caused to 1occur at non-consecutive two-stroke cycles and the 2interruptions in the sequence of injection from cylinder to cylinder are caused to occur non-consecutively. I 2. The method set forth in claim 1 wherein said 2engine is of the six-cylinder type, and the interruptions 3and injections occur in the following repeated sequence: 4 interrupt, inject, inject, interrupt, inject. 1 3. The method set forth in claim 1 wherein said 2engine is of the four-cylinder type, and the interruptions 3 nd injections occur in the following repeated sequence: 4inject, interrupt, inject, inject, interrupt. 1 4. In a multiple cylinder two-stroke fuel-injected 2internal combustion engine which comprises means for 3 causing operation at non-idle in a manner such that the 4fuel is injected into each cylinder during the fuel 5injection stage of consecutive two-stroke cycles of the 6 cylinder, the means for operating the engine at idle which -comprises means for interrupting the fuel injection stages 9operation in such a pattern that over a certain number of 0engine crankshaft revolutions the interruptions in each 1individual cylinder are caused to occur at non-consecutive 2two-stroke cycles and the interruptions in the sequence of 3injection from cylinder to cylinder are caused to occur 4non-consecutively. 1 5. The means for operating the engine at idle as set 2forth in claim 4 wherein said engine is of the 3six-cylinder type, and the means for interrupting the fuel 4injection stages of the cylinders comprises means for 5causing the injections and interruptions to occur in the 6following repeated sequence: interrupt, inject, inject, 7interrupt, inject. 1 6. The means for operating the engine at idle as set 2forth in claim 4 wherein said engine is of the 3four-cylinder type, and the means for interrupting the fuel injection stages of the cylinders comprises means for 5causing the interruptions and injections to occur in the 6following repeated sequence: inject, interrupt, inject, 7inject, interrupt. 1 7. In a multiple cylinder two-stroke fuel-injected 2internal combustion engine which operates at non-idle in a 3manner such that the fuel is injected into each cylinder during the fuel injection stage of consecutive two-stroke cycles of the cylinder, the method for operating the 6engine at idle which comprises interrupting the fuel 7injection stages of the cylinders from that which occurs 8at non-idle engine operation in such a pattern that over a 9 certain number of engine crankshaft revolutions the injections into each individual cylinder are caused to i occur at non-consecutive two-stroke cycles and the injections in the .sequence of injection from cylinder to cylinder are caused to occur non-consecutively. 8. The method set forth in claim 7 wherein said engine is of the six-cylinder type, and the interruptions and injections occur in the following repeated sequence: inject, interrupt, interrupt, inject, interrupt. 9. The method set forth in claim 7 wherein said engine is of the four-cylinder type, and the interruptions and injections occur in the following repeated sequence: interrupt, inject, interrupt, interrupt, inject. 10. In a multiple cylinder two-stroke fuel-injected internal combustion engine which comprises means for causing operation at non-idle in a manner such that the fuel is injected into each cylinder during the fuel injection stage of consecutive two-stroke cycles of the cylinder, the means for operating the engine at idle which comprises means for interrupting the fuel injection stages of the cylinders from that which occurs at non-idle engine operation in such a pattern that over a certain number of engine crankshaft revolutions the injections in each individual cylinder are caused to occur at non-consecutive two-stroke cycles and the injections in the sequence of injection from cylinder to cylinder are caused to occur non-consecutively. 11. The means for operating the engine at idle as set forth in claim 10 wherein said engine is of the six-cylinder type, and the means for interrupting the fuel injection stages of the cylinders comprises means for causing the injections and interruptions to occur in the following repeated sequence: inject, interrupt, interrupt, inject, interrupt. 1 12. The means for operating the engine at idle as 2set forth in claim 10 wherein said engine is of the 3four-cylinder type, and the means for interrupting the fuel injection stages of the cylinders comprises means for 5causing the interruptions and injections to occur in the 6following repeated sequence: interrupt, inject, interrupt, 7interrupt, inject. 1 13. In a multiple cylinder two-stroke fuel-injected 2internal combustion, means for operating the engine at 3idle which comprises means for interrupting the fuel 4injection stages in a predetermined pattern such that over 5a certain number of engine crankshaft revolutions a fewer 6number of injection stages occur than over the same number 7of engine crankshaft revolutions during non-idle 8operation, and means for increasing the quantity of fuel 9injected per injection stage relative to the quantity of 0 uel required per injection stage to secure idle operation 1without any injection interruptions. 1 14. Means as set forth in claim 13 including means 2for advancing the spark timing during idle operation in 3comparison to the spark timing that is appropriate for 4idle operation without any interruption of the injection stages. 1 15. In a multiple cylinder two-stroke fuel-injected 2internal combustion, the method of operating the engine at 3idle which comprises interrupting the fuel injection 4stages in a predetermined pattern such that over a certain 5 number of engine crankshaft revolutions a fewer number of 6 injection stages occur than over the same number of engine ηcrankshaft revolutions during non-idle operation, and 8 increasing the quantity of fuel injected per injection stage relative to the quantity of fuel required per injection stage to secure idle operation without any injection interruptions. 16. The method as set forth in claim 15 including advancing the spark timing during idle operation in comparison to the spark timing that is appropriate for idle operation without any interruption of the injection stages.

Inventors: BROOKS MARK ALLEN, DALY PAUL DESMOND, FALLIS ROBERT EDWARD, VERNER DOUGLAS ROBERT, BROOKS, MARK, ALLEN, DALY, PAUL, DESMOND, FALLIS, ROBERT, EDWARD, VERNER, DOUGLAS, ROBERT
Applicants: SIEMENS AG, SIEMENS AKTIENGESELLSCHAFT
Application year: 1990
Main classification: F02D41
IPC codes: F02D41