Apparatus and method for internal combustion engine control

• US 5,657,625 A
• Filed: 06/13/1995
• Issued: 08/19/1997
• Est. Priority Date: 06/17/1994
• Status: Expired due to Term

• Current Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Original Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Inventors: Kodama, Yoshiaki, Hirako, Osamu, Sanbayashi, Daisuke, Ohmori, Shogo, Okada, Kojiro, Koga, Kazuo, Togai, Kazuhide, Danno, Yoshiaki
• Primary Examiner(s): Kwon, Joan T.
• Application Number:
  US08/490,077
• Time in Patent Office: 798 Days
• Field of Search: 60/274, 60/285, 60/247, 60/286, 60/300
• US Class Current: 60/274
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 13/011 having two or more purifying devices arranged in parallel
• CPC Class Codes: F01N 13/08 Other arrangements or adaptations of exhaust conduits pipes, joints or supports therefor in general F16L; collecting or removing exhaust gases of vehicle engines in workshops B08B15/00, on highways E01C1/005
• CPC Class Codes: F01N 2250/12 absorption or adsorption, and catalytic conversion
• CPC Class Codes: F01N 2260/04 for regeneration or reactivation, e.g. of catalyst
• CPC Class Codes: F01N 2260/14 for modifying or adapting flow area or back-pressure
• CPC Class Codes: F01N 2410/00 By-passing, at least partially, exhaust from inlet to outlet of apparatus, to atmosphere or to other device
• CPC Class Codes: F01N 2430/06 by varying fuel-air ratio, e.g. by enriching fuel-air mixture
• CPC Class Codes: F01N 2570/04 Sulfur or sulfur oxides
• CPC Class Codes: F01N 2570/12 Hydrocarbons
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• CPC Class Codes: F01N 2900/102 Travelling distance
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/0871 Regulation of absorbents or adsorbents, e.g. purging by electrically controlling the supply of combustible mixture or its constituents only F02D41/0235
• CPC Class Codes: F01N 3/0885 Regeneration of deteriorated absorbents or adsorbents, e.g. desulfurization of NOx traps
• CPC Class Codes: F01N 3/18 characterised by methods of operation; Control
• CPC Class Codes: F01N 3/20 specially adapted for catalytic conversion F01N3/22 takes precedence; Methods of operation or control of catalytic converters
• CPC Class Codes: F01N 3/2006 Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating by electrically controlling the supply of combustible mixture or its constituents only F02D41/0235
• CPC Class Codes: F01N 3/2033 using a fuel burner or introducing fuel into exhaust duct
• CPC Class Codes: F01N 3/30 : Arrangements for supply of additional air control, e.g. using by-passes or variable air pump drives, F01N3/22
• CPC Class Codes: F01N 3/36 : Arrangements for supply of additional fuel
• CPC Class Codes: F01N 3/38 : Arrangements for igniting
• CPC Class Codes: F01N 9/005 : using models instead of sensors to determine operating characteristics of exhaust systems, e.g. calculating catalyst temperature instead of measuring it directly
• CPC Class Codes: F02D 2200/0802 : Temperature of the exhaust gas treatment apparatus
• CPC Class Codes: F02D 35/0015 : using exhaust gas sensors F02D41/14 takes precedence
• CPC Class Codes: F02D 41/0082 : per groups or banks F02D41/0087 takes precedence
• CPC Class Codes: F02D 41/0275 : the exhaust gas treating apparatus being a NOx trap or adsorbent
• CPC Class Codes: F02D 41/028 : Desulfurisation of NOx traps or adsorbent
• CPC Class Codes: F02D 41/187 : using a hot wire flow sensor
• CPC Class Codes: F02P 5/00 : Advancing or retarding ignition; Control therefor
• CPC Class Codes: Y02A 50/20 : Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 : Engine management systems

Abstract

An apparatus for controlling an internal combustion engine having an exhaust purifying catalytic device which absorbs nitrogen oxides contained in exhaust when the engine is in a lean-combustion mode and which deoxidizes the absorbed nitrogen oxides when the engine is in a rich-combustion mode. The engine control apparatus includes an electronic control unit for estimating the amount of purifying capability reducing substances other than nitrogen oxides, which decreases the nitrogen oxide adsorbing ability of the catalytic device, absorbed by the catalytic device, on the basis of the accumulated value of vehicle travel distance, fuel consumption of engine, or intake air amount. The control unit changes the operating condition of engine so that the exhaust gas temperature is increased when it is judged that the estimated adsorption amount has reached a predetermined adsorption amount. The exhaust purifying catalytic device is heated by high-temperature exhaust gas to remove the purifying capability reducing substances from the catalytic device.

Claims

1. A control apparatus for an internal combustion engine having an exhaust purifying catalytic device disposed in an exhaust passage for reducing emission of nitrogen oxides to atmosphere, the exhaust purifying catalytic device being operable to adsorb nitrogen oxides contained in exhaust gas discharged from the internal combustion engine when the engine is in a lean-combustion mode where an air-fuel ratio of an air-fuel mixture supplied to the engine is leaner than a theoretical air-fuel ratio, and to deoxidize adsorbed nitrogen oxides when the internal combustion engine is in a rich-combustion mode where the air-fuel ratio is equal to or richer than the theoretical air-fuel ratio, comprising:

adsorption amount estimating means for estimating an adsorption amount of purifying capability reducing substances, which decreases nitrogen oxide adsorbing ability of the exhaust purifying catalytic device, adsorbed by the exhaust purifying catalytic device and for determining whether the estimated adsorption amount has reached a predetermined adsorption amount; and

catalyst heating means for removing the purifying capability reducing substances from the exhaust purifying catalytic device by increasing a temperature of the exhaust purifying catalytic device by changing an operating condition of the internal combustion engine so that an exhaust gas temperature increases when said adsorption amount estimating means judges that the estimated adsorption amount has reached the predetermined adsorption amount.

2. A control apparatus according to claim 1, wherein said adsorption amount estimating means includes fuel amount accumulating means for accumulating fuel consumption of the internal combustion engine, and judges that the estimated adsorption amount has reached the predetermined adsorption amount when the accumulated fuel consumption calculated by said fuel amount accumulating means reaches a predetermined amount.

3. A control apparatus according to claim 2, wherein the internal combustion engine is supplied with fuel from a fuel injection valve driven by a pulse-shaped driving current, said fuel amount accumulating means accumulates a pulse width of the driving current, and said accumulated fuel consumption is calculated on the basis of the accumulated pulse width.

4. A control apparatus according to claim 2, wherein said fuel amount accumulating means accumulates the fuel consumption only when the internal combustion engine is being operated in the lean-combustion mode.

5. A control apparatus according to claim 2, further including:

catalyst temperature detecting means for detecting the temperature of the exhaust purifying catalytic device;

wherein said fuel amount accumulating means accumulates the fuel consumption only when the catalytic device temperature is not higher than a predetermined temperature.

6. A control apparatus according to claim 1, wherein said adsorption amount estimating means includes travel distance accumulating means for accumulating a travel distance of a vehicle on which the internal combustion engine is mounted, and judges that the estimated adsorption amount has reached the predetermined adsorption amount when the accumulated vehicle travel distance reaches a predetermined value.

7. A control apparatus according to claim 1, wherein said adsorption amount estimating means includes intake air amount accumulating means for detecting and accumulating an intake air amount of the internal combustion engine, and judges that the estimated adsorption amount has reached the predetermined adsorption amount when the accumulated intake air amount reaches a predetermined value.

8. A control apparatus according to claim 1, wherein said catalyst heating means burns fuel near the exhaust purifying catalytic device by changing the operating condition of the internal combustion engine so that fuel and air are supplied into the exhaust gas, by which the exhaust purifying catalytic device is heated by increasing the exhaust gas temperature.

9. A control apparatus according to claim 8, wherein said catalyst heating means includes air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine, and said air-fuel ratio control means controls the air-fuel ratio in part of cylinders of the internal combustion engine to a value lower than the theoretical air-fuel ratio to perform rich-combustion operation in said part of cylinders and controls the air-fuel ratio in the remaining cylinders to a value higher than the theoretical air-fuel ratio to perform lean-combustion operation in said remaining cylinders, by which the fuel and air are supplied into the exhaust gas.

10. A control apparatus according to claim 9, wherein said air-fuel ratio control means makes an average air-fuel ratio of all the cylinders of the internal combustion engine substantially equal to the theoretical air-fuel ratio when the exhaust purifying catalytic device is heated.

11. A control apparatus according to claim 9, wherein said air-fuel ratio control means includes catalyst temperature detecting means for detecting a temperature of the exhaust purifying catalytic device, and controls the air-fuel ratio so that the catalytic device temperature is kept at a predetermined temperature after the detected catalytic device temperature has increased to the predetermined temperature.

12. A control apparatus according to claim 11, wherein said air-fuel ratio control means makes an average air-fuel ratio of all the cylinders of the internal combustion engine substantially equal to the theoretical air-fuel ratio before the detected catalytic device temperature reaches said predetermined temperature, and corrects the average air-fuel ratio to a side richer than the theoretical air-fuel ratio after the predetermined temperature has been reached.

13. A control apparatus according to claim 9, wherein the internal combustion engine is a V-type engine, and said part of cylinders are on one bank side of said V-type engine, and said remaining cylinders are on the other bank side.

14. A control apparatus according to claim 9, wherein said air-fuel ratio control means includes ignition timing control means for controlling ignition timing of the internal combustion engine, and said ignition timing control means retards the ignition timing of said part of cylinders in which the rich-combustion operation is performed and advances the ignition timing of said remaining cylinders in which the lean-combustion operation is performed.

15. A control apparatus according to claim 9, wherein said air-fuel ratio control means includes intake air amount regulating means, and said intake air amount regulating means increases an intake air amount of the internal combustion engine when the rich-combustion operation is performed in said part of cylinders of the internal combustion engine and the lean-combustion operation is performed in the remaining cylinders.

16. A control apparatus according to claim 1, further including:

a lockup clutch interposed between the internal combustion engine and an automatic transmission; and

clutch control means for changing over said lockup clutch between a connected state in which the engine is connected directly to the automatic transmission and a disconnected state in which the engine is not connected directly to the automatic transmission;

wherein said clutch control means makes said lockup clutch disconnected during the time when the temperature of the exhaust purifying catalytic device is raised by said catalyst heating means.

17. A control apparatus according to claim 1, further including:

operating condition detecting means for detecting an operating condition of the internal combustion engine;

wherein said catalyst heating means heats the exhaust purifying catalytic device when said operating condition detecting means judges that the internal combustion engine is in a predetermined medium or heavy load operating condition.

18. A control apparatus according to claim 17, wherein said operating condition detecting means includes exhaust temperature estimating means for estimating an exhaust temperature of the internal combustion engine, and said operating condition detecting means judges that the internal combustion engine is in said predetermined medium or heavy load operating condition when the estimated exhaust temperature is not lower than a predetermined temperature.

19. A control apparatus according to claim 18, wherein said exhaust temperature estimating means includes load detecting means for detecting a load of the internal combustion engine and rotational speed detecting means for detecting a rotational speed of the internal combustion engine, and said exhaust temperature estimating means estimates said exhaust temperature on the basis of the detected engine load and the detected engine rotational speed.

20. A control apparatus according to claim 17, further including:

time measuring means for accumulatively measuring a time period elapsed during the time when said operating condition detecting means judges that the internal combustion engine is in said predetermined medium or heavy load operating condition, and said catalyst heating means heats the exhaust purifying catalytic device until the counted elapsed time period reaches a predetermined time.

21. A control apparatus according to claim 20, further including:

catalyst temperature detecting means for detecting the temperature of the exhaust purifying catalytic device;

wherein said time measuring means accumulatively measures said elapsed time period when the detected catalyst device temperature is not lower than a predetermined temperature.

22. A control apparatus according to claim 20, wherein said time measuring means starts to accumulatively measure said elapsed time period from a moment when a predetermined delay time has elapsed after said operating condition detecting means judges that the internal combustion engine is in said predetermined medium or heavy load operating condition.

23. A control apparatus according to claim 1, wherein said adsorption amount estimating means includes storage means for storing the estimated adsorption amount of the purifying capability reducing substances as long as said storage means is connected to a power source and power is supplied from said power source, and said catalyst heating means heats the exhaust purifying catalytic device independently of the estimated adsorption amount when the supply of power from said power source to said storage means is restarted after the power is not supplied from said power source to said storage means.

24. A control apparatus according to claim 1, wherein said catalyst heating means increases the exhaust gas temperature by changing a burning state of the internal combustion engine.

25. A control apparatus according to claim 24, wherein said catalyst heating means includes ignition timing correcting means for correcting ignition timing of the internal combustion engine, and said ignition timing correcting means changes the burning state of the internal combustion engine by retarding the ignition timing of the internal combustion engine.

26. A control apparatus according to claim 25, wherein said catalyst heating means includes intake air amount correcting means for correcting an intake air amount of the internal combustion engine, and said intake air amount correcting means increases the intake air amount during the time when said ignition timing correcting means retards the ignition timing.

27. A control apparatus according to claim 25, further including:

rotational speed detecting means for detecting a rotational speed of the internal combustion engine; and

volumetric efficiency detecting means for detecting a volumetric efficiency of the internal combustion engine;

wherein said ignition timing correcting means sets a retard amount of the ignition timing on the basis of the detected engine rotational speed and the detected volumetric efficiency.

28. A control apparatus according to claim 1, wherein said catalyst heating means includes catalyst temperature detecting means for detecting the temperature of the exhaust purifying catalytic device and air-fuel ratio control means for controlling the internal combustion engine so that the internal combustion engine is operated in a rich-combustion mode in which the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is equal to or richer than the theoretical air-fuel ratio, when the detected catalytic device temperature reaches a predetermined temperature.

29. A control apparatus according to claim 1, wherein said catalyst heating means includes air-fuel control means for controlling the internal combustion engine so that the internal combustion engine is operated in a rich-combustion mode in which the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is equal to or richer than the theoretical air-fuel ratio, when said adsorption amount estimating means judges that the adsorption amount of the purifying capability reducing substances has reached the predetermined adsorption amount;

and secondary air supplying means for supplying secondary air to an upstream side with respect to the exhaust purifying catalytic device in the exhaust passage when the internal combustion engine is controlled so that the internal combustion engine is operated in the rich-combustion mode.

30. A control apparatus according to claim 29, wherein said catalyst heating means includes catalyst temperature detecting means for detecting the temperature of the exhaust purifying catalytic device, and said secondary air supplying means decreases a supply amount of the secondary air when the detected catalytic device temperature reaches a predetermined temperature.

31. A control apparatus according to claim 29, further including:

rotational speed detecting means for detecting a rotational speed of the internal combustion engine; and

volumetric efficiency detecting means for detecting a volumetric efficiency of the internal combustion engine;

wherein said air-fuel ratio control means sets the air-fuel ratio during the time the internal combustion engine is operated in the rich-combustion mode on the basis of the detected engine rotational speed and the detected volumetric efficiency.

32. A control apparatus according to claim 29, further including:

rotational speed detecting means for detecting rotational speed of the internal combustion engine; and

volumetric efficiency detecting means for detecting a volumetric efficiency of the internal combustion engine;

wherein said secondary air supplying means sets a supply amount of the secondary air on the basis of the detected engine rotational speed and the detected volumetric efficiency.

33. A control apparatus according to claim 1, wherein said catalyst heating means increases the exhaust gas temperature by changing a flow velocity of the exhaust gas.

35. A control apparatus according to claim 33, wherein said catalyst heating means includes catalyst temperature detecting means for detecting the temperature of the exhaust purifying catalytic device and fuel supplying means for supplying fuel to an upstream side with respect to the exhaust purifying catalytic device in the exhaust passage when the detected catalyst temperature reaches a predetermined temperature.

36. A control apparatus according to claim 1, further including:

exhaust pipe length changing means for changing an exhaust passage length from an exhaust port of the internal combustion engine to the exhaust purifying catalytic device so that said exhaust pipe length changing means is controlled in such a manner that, when said adsorption amount estimating means judges that the adsorption amount of the purifying capability reducing substances has reached the predetermined adsorption amount, the exhaust passage length is shorter than that before it is judged that the estimated adsorption amount has reached the predetermined adsorption amount, by which the temperature of exhaust gas supplied to the exhaust purifying catalytic device is increased.

37. A control apparatus according to claim 36, wherein said exhaust pipe length changing means includes a first exhaust passage forming at least part of the exhaust passage extending from the exhaust port of the internal combustion engine to the exhaust purifying catalytic device, a second exhaust passage disposed in parallel with said first exhaust passage and shorter than said first exhaust passage, and valve means for opening and closing said second exhaust passage;

wherein said exhaust heating means closes said second exhaust passage by using said valve means before said adsorption amount estimating means judges that the estimated adsorption amount has reached the predetermined adsorption amount, and drives said valve means to open said second exhaust passage when said adsorption amount estimating means judges that the estimated adsorption amount has reached the predetermined adsorption amount, by which the exhaust gas is supplied to the exhaust purifying catalytic device via said second exhaust passage.

38. A control apparatus according to claim 36, wherein the exhaust purifying catalytic device is disposed near a body of the internal combustion engine.

39. A control apparatus according to claim 36, wherein said catalyst heating means includes catalyst temperature detecting means for detecting the temperature of the exhaust purifying catalytic device, and fuel supplying means for supplying fuel to an upstream side with respect to the exhaust purifying catalytic device in the exhaust passage when the detected catalyst temperature reaches a predetermined temperature.

34. A control apparatus according to claim wherein said catalyst heating means includes an exhaust throttle valve, installed on a downstream side with respect to the exhaust purifying catalytic device in the exhaust passage, for changing an area of the exhaust passage, and said catalyst heating means changes the flow velocity of the exhaust gas by controlling said exhaust throttle valve so that the exhaust passage area is decreased.

40. A control apparatus for an internal combustion engine having an exhaust purifying catalytic device disposed in an exhaust passage for reducing emission of nitrogen oxides to atmosphere, the exhaust purifying catalytic device being operable to adsorb nitrogen oxides contained in exhaust gas discharged from the internal combustion engine when the engine is in a lean-combustion mode where an air-fuel ratio of an air-fuel mixture supplied to the engine is leaner than a theoretical air-fuel ratio, and to deoxidize adsorbed nitrogen oxides when the internal combustion engine is in a rich-combustion mode where the air-fuel ratio is equal to or richer than the theoretical air-fuel ratio, comprising:

a burner, disposed near the exhaust purifying catalytic device, for heating the exhaust purifying catalytic device;

adsorption amount estimating means for estimating an adsorption amount of purifying capability reducing substances, which decreases nitrogen oxide adsorbing ability of the exhaust purifying catalytic device, adsorbed by the exhaust purifying catalytic device, and for determining whether the estimated adsorption amount has reached a predetermined adsorption amount; and

catalyst heating means for removing the purifying capability reducing substances from the exhaust purifying catalytic device by activating said burner when said adsorption amount estimating means judges that the adsorption amount of the purifying capability reducing substances has reached the predetermined adsorption amount.

41. An internal combustion engine control method for reducing emission of nitrogen oxides to atmosphere, by causing nitrogen oxides, contained in exhaust gas discharged from the internal combustion engine, to be adsorbed by an exhaust purifying catalytic device, disposed in an exhaust passage of the internal combustion engine, when the engine is in a lean-combustion mode where an air-fuel ratio of an air-fuel mixture supplied to the engine is leaner than a theoretical air-fuel ratio, and by deoxidizing adsorbed nitrogen oxides by means of the exhaust purifying catalytic device when the internal combustion engine is in a rich-combustion mode where the air-fuel ratio is equal to or richer than the theoretical air-fuel ratio, comprising the steps of:

(a) estimating an adsorption amount of purifying capability reducing substances, which decreases nitrogen oxide adsorbing ability of the exhaust purifying catalytic device, adsorbed by the exhaust purifying catalytic device, and determining whether the estimated adsorption amount has reached a predetermined adsorption amount; and

(b) removing the purifying capability reducing substances from the exhaust purifying catalytic device by increasing a temperature of the exhaust purifying catalytic device by changing an operating condition of the internal combustion engine so that an exhaust gas temperature increases when it is judged in said step (a) that the estimated adsorption amount has reached the predetermined adsorption amount.

42. An internal combustion engine control method according to claim 41, wherein said step (a) includes the sub-steps of:

(a1) accumulating fuel consumption of the internal combustion engine; and

(a2) judging that the estimated adsorption amount has reached the predetermined adsorption amount when the accumulated fuel consumption calculated in said sub-step (a1) reaches a predetermined value.

43. An internal combustion engine control method according to claim 42, wherein said sub-step (a1) includes accumulating a pulse width of a driving current supplied to a fuel injection valve installed on the internal combustion engine, and calculating said accumulated fuel consumption on the basis of the accumulated pulse width.

44. An internal combustion engine control method according to claim 42, wherein said sub-step (a1) includes accumulating the fuel consumption only when the internal combustion engine is operated in the lean-combustion mode.

45. An internal combustion engine control method according to claim 42, further including the sub-step of:

(a3) detecting the temperature of the exhaust purifying catalytic device;

wherein said sub-step (a1) includes accumulating the fuel consumption only when the catalytic device temperature detected in said sub-step (a3) is not higher than a predetermined temperature.

46. An internal combustion engine control method according to claim 41, wherein said step (a) includes the sub-steps of:

(a1) determining an accumulated value of a travel distance of a vehicle on which the internal combustion engine is mounted; and

(a2) judging that the estimated adsorption amount has reached the predetermined adsorption amount when the accumulated value of the vehicle travel distance determined in said sub-step (a1) reaches a predetermined value.

47. An internal combustion engine control method according to claim 41, wherein said step (a) includes the sub-steps of:

(a1) determining an accumulated value of an intake air amount by detecting the intake air amount of the internal combustion engine; and

(a2) judging that the estimated adsorption amount has reached the predetermined adsorption amount when the accumulated value of the intake air amount determined in said sub-step (a1) reaches a predetermined value.

48. An internal combustion engine control method according to claim 41, wherein said step (b) includes burning fuel in the vicinity of the exhaust purifying catalytic device by changing the operating condition of the internal combustion engine so that fuel and air are supplied into the exhaust gas, by which the exhaust gas temperature is increased to heat the exhaust purifying catalytic device.

49. An internal combustion engine control method according to claim 48, wherein said step (b) includes controlling the air-fuel ratio in part of cylinders of the internal combustion engine to a value lower than the theoretical air-fuel ratio and controlling the air-fuel ratio in the remaining cylinders to a value higher than the theoretical air-fuel ratio, by which rich-combustion operation is performed in said part of cylinders and lean-combustion operation is performed in said remaining cylinders to supply the fuel and air into the exhaust gas.

50. An internal combustion engine control method according to claim 49, wherein said step (b) includes making an average air-fuel ratio of all the cylinders of the internal combustion engine substantially equal to the theoretical air-fuel ratio when the exhaust purifying catalytic device is heated.

51. An internal combustion engine control method according to claim 49, wherein said step (b) includes the sub-steps of:

(b1) detecting the temperature of the exhaust purifying catalytic device; and

(b2) controlling the air-fuel ratio so that the catalytic device temperature is kept at a predetermined temperature after the catalytic device temperature detected in said sub-step (b1) has increased to said predetermined temperature.

52. An internal combustion engine control method according to claim 51, wherein said sub-step (b2) includes making the average air-fuel ratio of all the cylinders of the internal combustion engine substantially equal to the theoretical air-fuel ratio before the catalytic device temperature detected in said sub-step (b1) and correcting the average air-fuel ratio to a side richer than the theoretical air-fuel ratio after the predetermined temperature has been reached.

53. An internal combustion engine control method according to claim 49, wherein said step (b) includes controlling the air-fuel ratio for cylinders on one bank side of a V-type engine to a value lower than the theoretical air-fuel ratio and controlling the air-fuel ratio for cylinders on the other bank side of said V-type engine to a value higher than the theoretical air-fuel ratio, by which the rich-combustion operation is performed in the cylinders on said one bank side and the lean-combustion operation is performed in the cylinders on said other band side.

54. An internal combustion engine control method according to claim 49, further including the step of:

(c) retarding ignition timing of said part of cylinders in which the rich-combustion operation is performed and advancing the ignition timing of said remaining cylinders in which the lean-combustion operation is performed.

55. An internal combustion engine control method according to claim 49, further including the step of:

(c) increasing an intake air amount of the internal combustion engine when the rich-combustion operation is performed in said part of cylinders of the internal combustion engine and the lean-combustion operation is performed in the remaining cylinders.

56. An internal combustion engine control method according to claim 41, further including the step of:

(c) disconnecting an automatic transmission from the internal combustion engine by means of a lockup clutch during the time when the temperature of the exhaust purifying catalytic device is raised in said step (b), the lockup clutch being operable to change over a connecting condition between the internal combustion engine and the automatic transmission between a connected state and a disconnected state.

57. An internal combustion engine control method according to claim 41, wherein said step (b) includes the sub-steps of:

(b1) detecting an operating condition of the internal combustion engine; and

(b2) heating the exhaust purifying catalytic device when it is judged that the internal combustion engine is in a predetermined medium or heavy load operating condition in said sub-step (b1).

58. An internal combustion engine control method according to claim 57, wherein said sub-step (b1) includes the sub-steps of:

(b11) estimating an exhaust temperature of the internal combustion engine; and

(b12) judging that the internal combustion engine is in said predetermined medium or heavy load operating condition when the estimated exhaust temperature is not lower than a predetermined temperature.

59. An internal combustion engine control method according to claim 58, wherein said sub-step (b11) includes the sub-steps of:

(b111) detecting a load of the internal combustion engine;

(b112) detecting a rotational speed of the internal combustion engine; and

(b113) estimating said exhaust temperature on the basis of the engine load detected in said sub-step (b111) and the engine rotational speed detected in said sub-step (b112).

60. An internal combustion engine control method according to claim 57, further including the sub-step of:

(b3) accumulatively measuring a time period elapsed during the time when it is judged that the internal combustion engine is in said predetermined medium or heavy load operating condition;

wherein said step (b2) includes heating the exhaust purifying catalytic device until the elapsed time period measured in said step (b3) reaches a predetermined time.

61. An internal combustion engine control method according to claim 60, further including the sub-step of:

(b4) detecting the temperature of the exhaust purifying catalytic device;

wherein said sub-step (b3) includes accumulatively measuring said elapsed time period when the catalytic device temperature detected in said sub-step (b4) is not lower than a predetermined temperature.

62. An internal combustion engine control method according to claim 60, wherein said sub-step (b3) includes starting to accumulatively measure the elapsed time period from a moment when a predetermined delay time has elapsed after it is judged that the internal combustion engine is in said predetermined medium or heavy load operating condition in said sub-step (b1).

63. An internal combustion engine control method according to claim 41, further including the steps of:

(c) storing the estimated adsorption amount of the purifying capability reducing substances;

(d) heating the exhaust purifying catalytic device independently of the estimated adsorption amount when the storage of estimated adsorption amount of the purifying capability reducing substances becomes possible again after the storage of estimated adsorption amount of the purifying capability reducing substances has become impossible in said step (c).

64. An internal combustion engine control method according to claim 41, wherein said step (b) includes increasing the exhaust gas temperature by changing a burning state of the internal combustion engine.

65. An internal combustion engine control method according to claim 64, wherein said step (b) includes changing the burning state of the internal combustion engine by retarding ignition timing of the internal combustion engine.

66. An internal combustion engine control method according to claim 65, further including the step of:

(c) increasing an intake air amount during the time when the ignition timing of the internal combustion engine is retarded in said step (b).

67. An internal combustion engine control method according to claim 65, further including the steps of:

(c) detecting a rotational speed of the internal combustion engine; and

(d) detecting a volumetric efficiency of the internal combustion engine;

wherein said step (b) includes setting a retard amount of the ignition timing on the basis of the engine rotational speed detected in said step (c) and the volumetric efficiency detected in said step (d).

68. An internal combustion engine control method according to claim 41, further including the steps of:

(c) detecting the temperature of the exhaust purifying catalytic device; and

(d) controlling the internal combustion engine so that the internal combustion engine is operated in a rich-combustion mode in which the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is equal to or richer than the theoretical air-fuel ratio, when the catalytic device temperature detected in said step (c) reaches a predetermined temperature.

69. An internal combustion engine control method according to claim 41, wherein said step (b) includes the sub-steps of:

(b1) controlling the internal combustion engine so that the internal combustion engine is operated in a rich-combustion mode in which the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is equal to or richer than the theoretical air-fuel ratio, when it is judged that the estimated adsorption amount has reached the predetermined adsorption amount in said step (a); and

(b2) supplying secondary air to an upstream side with respect to the exhaust purifying catalytic device in the exhaust passage when the internal combustion engine is controlled in said sub-step (b1) so that the internal combustion engine is operated in the rich-combustion mode.

70. An internal combustion engine control method according to claim 69, wherein said step (b) includes the sub-step of:

(b3) detecting the temperature of the exhaust purifying catalytic device;

wherein said sub-step (b2) includes decreasing a supply amount of the secondary air when the catalytic device temperature detected in said sub-step (b3) reaches a predetermined temperature.

71. An internal combustion engine control method according to claim 69, further including the steps of:

(c) detecting a rotational speed of the internal combustion engine; and

(d) detecting a volumetric efficiency of the internal combustion engine;

wherein said sub-step (b1) includes setting the air-fuel ratio during the time the internal combustion engine is operated in the rich-combustion mode on the basis of the engine rotational speed detected in said step (c) and the volumetric efficiency detected in said step (d).

72. An internal combustion engine control method according to claim 69, further including the steps of:

(c) detecting a rotational speed of the internal combustion engine; and

(d) detecting a volumetric efficiency of the internal combustion engine;

wherein said step (b2) includes setting a supply amount of the secondary air on the basis of the engine rotational speed detected in said step (c) and the volumetric efficiency detected in said step (d).

73. An internal combustion engine control method according to claim 41, wherein said step (b) includes increasing the exhaust gas temperature by changing a flow velocity of the exhaust gas discharged from the internal combustion engine.

74. An internal combustion engine control method according to claim 73, wherein said step (b) includes changing the flow velocity of the exhaust gas by decreasing a passage area on a downstream side with respect to the exhaust purifying catalytic device in the exhaust passage.

75. An internal combustion engine control method according to claim 73, further including the steps of:

(c) detecting the temperature of the exhaust purifying catalytic device; and

(d) supplying fuel to an upstream side with respect to the exhaust purifying catalytic device in the exhaust passage when the catalyst temperature detected in said step (c) reaches a predetermined temperature.

76. An internal combustion engine control method according to claim 41, wherein said step (b) includes making an exhaust passage length from an exhaust port of the internal combustion engine to the exhaust purifying catalytic device shorter than that before it is judged that the predetermined adsorption amount has been reached when it is judged that the estimated adsorption amount has reached the predetermined adsorption amount in said step (a), by which the temperature of the exhaust gas supplied to the exhaust purifying catalytic device is increased.

77. An internal combustion engine control method according to claim 76, further including the steps of:

(c) detecting the temperature of the exhaust purifying catalytic device; and

(d) supplying fuel to an upstream side with respect to the exhaust purifying catalytic device in the exhaust passage when the catalyst temperature detected in said step (c) reaches a predetermined temperature.