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EP-3572648-B1 - SPARK ASSISTED COMPRESSION-IGNITION ENGINE CONTROL

EP3572648B1EP 3572648 B1EP3572648 B1EP 3572648B1EP-3572648-B1

Inventors

  • Sueoka, Masanari
  • INOUE, ATSUSHI
  • MARUYAMA, KEIJI
  • OHURA, TAKUYA
  • NISHIDA, TOMOHIRO
  • KAWAI, YUSUKE
  • CHIKADA, Tetsuya
  • TOKUNAGA, TATSUHIRO

Dates

Publication Date
20260506
Application Date
20190516

Claims (13)

  1. A method of implementing control logic for a compression-ignition engine (1), the engine (1) comprising: a fuel injection part (6) configured to inject fuel to be supplied into a combustion chamber (17); a variable valve operating mechanism (23, 24) configured to change a valve timing of an intake valve (21) and an exhaust valve (22); an ignition part (25) configured to ignite a mixture gas inside the combustion chamber (17); a supercharger (44) configured to boost gas introduced into the combustion chamber (17); an EGR system (55) comprising an EGR passage (52) connecting an intake passage (40) and an exhaust passage (50), an EGR cooler (53) and an EGR valve (54) disposed in the EGR passage (52) for adjusting a flow rate of the exhaust gas flowing through the EGR passage (52); a measurement part (SW1-17) configured to measure at least one parameter related to an operating state of the engine (1); and a control part (10) configured to perform a calculation according to a control logic corresponding to the operating state of the engine (1), in response to the measurement of the measurement part (SW1-17), and output a signal to the fuel injection part (6), the variable valve operating mechanism (23, 24), the ignition part (25), the EGR valve (54), and the supercharger (44), the control part (10) outputting the signal to the fuel injection part (6), the variable valve operating mechanism (23, 24) and the supercharger (44) so that an air-fuel ratio (A/F) that is a weight ratio of air contained in the mixture gas to the fuel becomes the stoichiometric air fuel ratio or richer than the stoichiometric air fuel ratio, while causing the supercharger (44) to boost, outputting the signal to the EGR valve (54) so that a gas-fuel ratio (G/F) that is a weight ratio of the entire gas of the mixture gas including air and EGR gas inside the combustion chamber (17) to the fuel becomes leaner than a stoichiometric air fuel ratio, and outputting the signal to the ignition part (25) so that an unburnt mixture gas combusts by self-ignition after the ignition part (25) ignites the mixture gas inside the combustion chamber (17) so as to achieve SPCCI (SPark Controlled Compression Ignition) combustion, the method of implementing the control logic comprising the steps of: determining a supercharging pressure P in kPa by the supercharger (44); and determining the control logic defining a close timing IVC in degrees after bottom dead center (deg.aBDC) of the intake valve (21), characterised in that the close timing IVC (deg.aBDC) is determined so that the supercharging pressure P (kPa) satisfies the following expression: 150 > = P > = 8.0 × 10 − 11 IVC 6 − 1.0 × 10 − 8 IVC 5 + 3.0 × 10 − 7 IVC 4 − 4.0 × 10 − 6 IVC 3 + 0.0068 IVC 2 − 0.3209 IVC + 116.63 .
  2. The method of claim 1, wherein the control part (10) determines a target supercharging pressure corresponding to the operating state of the engine (1), and wherein the control part (10) determines the close timing IVC (deg.aBDC) so that, when the target supercharging pressure is used as the supercharging pressure P (kPa), the supercharging pressure P (kPa) satisfies the expression and/or the close timing IVC of the intake valve (21) changes as the operating state of the engine (1) changes, and wherein the close timing IVC (deg.aBDC) is determined for each operating state so that the expression is satisfied.
  3. The method of any one of the preceding claims, wherein the engine (1) operates in a high-load operating state at a given load or higher or in a maximum load operating state.
  4. The method of any one of the preceding claims, wherein a geometric compression ratio å of the engine (1) is set so as to satisfy 10<=ε<21.
  5. The method of any one of the preceding claims, wherein the control part (10) outputs the signal to the EGR system (55) and the ignition part (25) so that a heat amount ratio used as an index related to a ratio of an amount of heat generated when the mixture gas inside the combustion chamber (17) combusts by flame propagation to the entire amount of heat generated when the mixture gas combusts, becomes a target heat amount ratio defined corresponding to the operating state of the engine (1), wherein the heat amount ratio is defined as an area of SI combustion (Qsi) per an area of CI combustion (Qci) in a waveform of the SPCCI combustion.
  6. The method of claim 5, wherein the control part (10) outputs a signal to the EGR system (55) and the ignition part (25) so that the heat amount ratio becomes higher when the load of the engine (1) is higher.
  7. A control device for a compression-ignition engine (1), the engine (1) comprising: a fuel injection part (6) configured to inject fuel to be supplied in a combustion chamber (17); a variable valve operating mechanism (23, 24) configured to change a valve timing of an intake valve (21) and an exhaust valve (22); an ignition part (25) configured to ignite a mixture gas inside the combustion chamber (17); a supercharger (44) configured to boost gas introduced into the combustion chamber (17); an EGR system (55) comprising an EGR passage (52) connecting an intake passage (40) and an exhaust passage (50), an EGR cooler (53) and an EGR valve (54) disposed in the EGR passage (52) for adjusting a flow rate of the exhaust gas flowing through the EGR passage (52); and a measurement part (SW1-17) configured to measure a parameter related to an operating state of the engine (1), the control device comprising: a control part (10) configured to perform a calculation according to a control logic corresponding to the operating state of the engine (1), in response to the measurement of the measurement part (SW1-17), and output a signal to the fuel injection part (6), the variable valve operating mechanism (23, 24), the ignition part (25), the EGR valve (54), and the supercharger (44), the control part (10) outputting the signal to the fuel injection part (6), the variable valve operating mechanism (23, 24) and the supercharger (44) so that an air-fuel ratio (A/F) that is a weight ratio of air contained in the mixture gas to the fuel becomes the stoichiometric air fuel ratio or richer than the stoichiometric air fuel ratio, while causing the supercharger (44) to boost, outputting the signal to the EGR valve (54) so that a gas-fuel ratio (G/F) that is a weight ratio of the entire gas including air and EGR gas of the mixture gas inside the combustion chamber (17) to the fuel becomes leaner than a stoichiometric air fuel ratio, and outputting the signal to the ignition part (25) so that an unburnt mixture gas combusts by self-ignition after the ignition part (25) ignites the mixture gas inside the combustion chamber (17) so as to achieve SPCCI (SPark Controlled Compression Ignition) combustion, wherein the control part (10) determines a supercharging pressure P in kPa by the supercharger (44), and determines a close timing IVC in degrees after bottom dead center (deg.aBDC) of the intake valve (21), characterised in that the control part (10) determines, according to the control logic, the close timing IVC (deg.aBDC) so that the supercharging pressure P (kPa) satisfies the following expression: 150 > = P > = 8.0 × 10 − 11 IVC 6 − 1.0 × 10 − 8 IVC 5 + 3.0 × 10 − 7 IVC 4 − 4.0 × 10 − 6 IVC 3 + 0.0068 IVC 2 − 0.3209 IVC + 116.63 .
  8. The control device of claim 7, wherein the control part (10) determines a target supercharging pressure corresponding to the operating state of the engine (1), and wherein the control part (10) determines the close timing IVC (deg.aBDC) so that, when the target supercharging pressure is used as the supercharging pressure P (kPa), the supercharging pressure P (kPa) satisfies the expression and/or the close timing IVC of the intake valve (21) changes as the operating state of the engine (1) changes, wherein the close timing IVC (deg.aBDC) is determined for each operating state so that the expression is satisfied.
  9. The control device of any one of the preceding claims 7 to 8, wherein the engine (1) operates in a high-load operating state at a given load or higher or in a maximum load operating state.
  10. The control device of any one of the preceding claims 7 to 9, wherein the geometric compression ratio ε of the engine (1) is set so as to satisfy 10<=ε<21.
  11. The control device of any one of the preceding claims 7 to 10, wherein the control part (10) outputs the signal to the EGR system (55) and the ignition part (25) so that a heat amount ratio used as an index related to a ratio of an amount of heat generated when the mixture gas inside the combustion chamber (17) combusts by flame propagation to the entire amount of heat generated when the mixture gas combusts, becomes a target heat amount ratio defined corresponding to the operating state of the engine (1) and/or the control part (10) outputs a signal to the EGR system (55) and the ignition part (25) so that the heat amount ratio becomes higher when the load of the engine (1) is higher, wherein the heat amount ratio is defined as an area of SI combustion (Qsi) per an area of CI combustion (Qci) in a waveform of the SPCCI combustion.
  12. A compression-ignition engine (1) comprising a fuel injection part (6) configured to inject fuel to be supplied in a combustion chamber (17); a variable valve operating mechanism (23, 24) configured to change a valve timing of an intake valve (21) and an exhaust valve (22); an ignition part (25) configured to ignite a mixture gas inside the combustion chamber (17); a supercharger (44) configured to boost gas introduced into the combustion chamber (17); an EGR system (55) comprising an EGR passage (52) connecting an intake passage (40) and an exhaust passage (50), an EGR cooler (53) and an EGR valve (54) disposed in the EGR passage (52) for adjusting a flow rate of the exhaust gas flowing through the EGR passage (52); a measurement part (SW1-17) configured to measure a parameter related to an operating state of the engine (1), and a control device according to any one of the preceding claims 7 to 11.
  13. A computer program product comprising computer-readable instructions, which when loaded and executed on the control device according to any one of the preceding claims 7 to 11, can perform the steps of any of the above-mentioned methods according to the preceding claims 1 to 6.

Description

TECHNICAL FIELD The technology disclosed herein relates to a method of controlling a compression-ignitioin engine, a control device for a compression-ignition engine, a computer program product and to a compression-ignition engine. BACKGROUND OF THE DISCLOSURE It is known that combustion by compressed self-ignition, in which a mixture gas combusts instantly without flame propagation, maximizes fuel efficiency since the combustion period is minimal. However, various problems must be solved for automobile engines with regard to combustion by compressed self-ignition. For example, since the operating states and the environmental conditions vary greatly in automotive applications, stabilizing compressed self-ignition is a major problem. The combustion by compressed self-ignition has not been put to practical use for the automobile engine yet. In order to solve the problem, for example, JP 4,082,292 B2 proposes that an ignition plug ignites the mixture gas, when compressed self-ignition hardly occurs because of a low combustion-chamber temperature. By igniting the mixture gas immediately before the compression top dead center, the pressure around the ignition plug increases to facilitate the compressed self-ignition. Unlike the technology disclosed in JP 4,082,292 B2 in which the compressed self-ignition is assisted by the ignition of the ignition plug, the present applicant rather proposes SPCCI (SPark Controlled Compression Ignition) combustion which is a combination of SI (Spark Ignition) combustion and CI (Compression Ignition) combustion. The SI combustion is combustion accompanied by the flame propagation initiated by forcibly igniting the mixture gas inside the combustion chamber. The CI combustion is combustion initiated by the mixture gas inside the combustion chamber carrying out the compressed self-ignition. The SPCCI combustion is combustion in which, when the mixture gas inside the combustion chamber is forcibly ignited to start the combustion by flame propagation, the unburnt mixture gas inside the combustion chamber combusts by the compression-ignition because of a pressure buildup due to the heat generation and the flame propagation of the SI combustion. Since the SPCCI combustion includes the CI combustion, it is one form of "the combustion by compression-ignition." The CI combustion takes place, when the in-cylinder temperature reaches an ignition temperature defined by the composition of the mixture gas. Fuel efficiency can be maximized, if the in-cylinder temperature reaches the ignition temperature near a compression top dead center and the CI combustion takes place. The in-cylinder temperature increases according to the increase in the in-cylinder pressure. The in-cylinder pressure in the SPCCI combustion is a result of two pressure buildups of a pressure buildup by the compression work of the piston in a compression stroke, and a pressure buildup caused by the heat generation of the SI combustion. Here, if the CI combustion takes place near a compression top dead center because of a high in-cylinder temperature at a compression starting timing due to a high ambient temperature, etc., the in-cylinder pressure excessively increases to create excessive combustion noise. In this case, combustion noise can be reduced if the ignition timing is retarded. However, if the ignition timing is retarded, since the CI combustion takes place when the piston falls considerably in the expansion stroke, fuel efficiency is decreased. Since the pressure buildup caused by the heat generation of the SI combustion can be utilized in the SPCCI combustion, for example, it is effective to lower the effective compression ratio and to reduce the pressure buildup by the compression work of the piston in order to achieve both the reduction of combustion noise and improvement in fuel efficiency. Thus, combustion noise can be kept suitable, without decreasing fuel efficiency. In order to put to practical use the engine which performs the SPCCI combustion, it is necessary to take into consideration other control factors relevant to the in-cylinder temperature, other than effective compression ratio. However, since the SPCCI combustion is a new combustion system, no one has found other control factors until now. Since the SPCCI combustion is compression-ignition combustion, combustion noise tends to be increased. The present inventors found that it was necessary to adjust the temperature inside the combustion chamber at the start timing of the CI combustion to a suitable temperature, in order to achieve a stable SPCCI combustion, while reducing combustion noise. If the temperature inside the combustion chamber is low, the ignitability of the CI combustion falls. Combustion noise increases as the temperature inside the combustion chamber goes up. The temperature inside the combustion chamber mainly depends on the geometric compression ratio of the engine, and the temperature and/or amount of gas introduced into the combusti