초록 ▼

A diesel engine (1) provided with a NOx catalyst ( 28A) and a diesel particulate filter (28B) performs lean burn operation during normal running, rich burn operation during regeneration of the NOx catalyst (28A), operation under the stoichiometric air-fuel ratio during desulphating of the NOx cataly

A diesel engine (1) provided with a NOx catalyst ( 28A) and a diesel particulate filter (28B) performs lean burn operation during normal running, rich burn operation during regeneration of the NOx catalyst (28A), operation under the stoichiometric air-fuel ratio during desulphating of the NOx catalyst (28A), and operation under a slightly lean air-fuel ratio to regenerate the filter after desulphating of the NOx catalyst (28A). When the lean burn operation is applied, a controller (31) first controls the fuel injection amount, and controls an air supply amount based on the fuel injection amount. When rich burn operation is applied, the controller ( 31) first controls the air supply amount and controls the fuel injection amount based on the air supply amount. Due to this control, the response of the excess air factor control is enhanced while preventing torque fluctuation accompanying the variation of the target excess air factor.

대표청구항 ▼

What is claimed is: 1. An excess air factor control method for a diesel engine which burns a mixture of air supplied by an air supply mechanism and fuel supplied by a fuel supply mechanism, comprising: detecting a running state of the diesel engine; setting a target excess air factor of the mixtur

What is claimed is: 1. An excess air factor control method for a diesel engine which burns a mixture of air supplied by an air supply mechanism and fuel supplied by a fuel supply mechanism, comprising: detecting a running state of the diesel engine; setting a target excess air factor of the mixture based on the running state; controlling an air supply amount of the air supply mechanism to a target air supply amount calculated from a predetermined fuel supply amount that has been determined without depending on the air supply amount of the air supply mechanism and the target excess air factor when the target excess air factor is larger than a value equivalent to a stoichiometric air-fuel ratio; and controlling a fuel supply amount of the fuel supply mechanism to a target fuel supply amount calculated from a predetermined air supply amount that has been determined without depending on the fuel supply amount of the fuel supply mechanism and the target excess air factor when the target excess air factor is smaller than the value equivalent to the stoichiometric air-fuel ratio. 2. An excess air factor control device for a diesel engine which burns a mixture of air supplied by an air supply mechanism and fuel supplied by a fuel supply mechanism, comprising: means for detecting a running state of the diesel engine; means for setting a target excess air factor of the mixture based on the running state; means for controlling an air supply amount of the air supply mechanism to a target air supply amount calculated from a predetermined fuel supply amount that has been determined without depending on the air supply amount of the air supply mechanism and the target excess air factor when the target excess air factor is larger than a value equivalent to a stoichiometric air-fuel ratio; and means for controlling a fuel supply amount of the fuel supply mechanism to a target fuel supply amount calculated from a predetermined air supply amount that has been determined without depending on the fuel supply amount of the fuel supply mechanism and the target excess air factor when the target excess air factor is smaller than the value equivalent to the stoichiometric air-fuel ratio. 3. An excess air factor control device for a diesel engine which burns a mixture of air supplied by an air supply mechanism and fuel supplied by a fuel supply mechanism, comprising: a sensor which detects a running state of the diesel engine; and a programmable controller programmed to: set a target excess air factor of the mixture based on the running state; control an air supply amount of the air supply mechanism to a target air supply amount calculated from a predetermined fuel supply amount that has been determined without depending on the air supply amount of the air supply mechanism and the target excess air factor when the target excess air factor is larger than a value equivalent to a stoichiometric air-fuel ratio; and control a fuel supply amount of the fuel supply mechanism to a target fuel supply amount calculated from a predetermined air supply amount that has been determined without depending on the fuel supply amount of the fuel supply mechanism and the target excess air factor when the target excess air factor is smaller than the value equivalent to the stoichiometric air-fuel ratio. 4. The excess air factor control device as defined in claim 3, wherein the running state detecting sensor further comprises a sensor which detects a load of the diesel engine and a sensor which detects a rotation speed of the diesel engine, and the controller is further programmed, when the target excess air factor is larger than the value equivalent to the stoichiometric air-fuel ratio equivalent value, to calculate a target engine torque based on the load of the diesel engine and the rotation speed of the diesel engine, calculate a target air amount basic value based on the target engine torque and the rotation speed of the diesel engine, calculate a conversion coefficient based on the target excess air factor and the rotation speed of the diesel engine, set the predetermined air supply amount equal to a value obtained by multiplying the target air amount basic value by the conversion coefficient, and control the air supply amount of the air supply mechanism to the predetermined air supply amount. 5. The excess air factor control device as defined in claim 3, wherein the running state detecting sensor comprises a sensor which detects a load of the diesel engine and a sensor which detects a rotation speed of the diesel engine, and the controller is further programmed, when the target excess air factor is less than the value equivalent to the stoichiometric air-fuel ratio, to calculate a target engine torque based on the load of the diesel engine and the rotation speed of the diesel engine, set a predetermined fuel supply amount equal to a value calculated based on the target engine torque and the rotation speed of the diesel engine, and control the fuel supply amount of the fuel supply mechanism to the predetermined fuel supply amount. 6. The excess air factor control device as defined in claim 3, wherein the running state detecting sensor comprises the controller which is further programmed to count a running time of the diesel engine. 7. The excess air factor control device as defined in claim 3, wherein the controller is further programmed to apply delay processing to the target excess air factor when the target excess air factor varies between a value larger than the value equivalent to the stoichiometric air-fuel ratio and a value which is not larger than the value equivalent to the stoichiometric air-fuel ratio. 8. The excess air factor control device as defined in claim 3, wherein the air supply mechanism comprises a variable geometry turbocharger, and the controller is further programmed to control the air supply amount by varying a turbocharging pressure of the variable geometry turbocharger. 9. The excess air factor control device as defined in claim 3, wherein the air supply mechanism comprises an exhaust gas recirculation valve which recirculates a part of an exhaust gas of the diesel engine into the air supplied by the air supply mechanism, and the controller is further programmed to control the air supply amount by varying an exhaust gas recirculation amount of the exhaust gas recirculation valve. 10. The excess air factor control device as defined in claim 3, wherein the diesel engine comprises an intake passage, the air supply mechanism comprises an intake throttle provided in the intake passage, and the controller is further programmed to control the air supply amount by varying a throttle opening of the intake throttle. 11. The excess air factor control device as defined in claim 1, wherein the diesel engine comprises a nitrogen oxide trap catalyst which traps nitrogen oxides in an exhaust gas of the diesel engine when an excess air factor of the mixture is larger than the value equivalent to the stoichiometric air-fuel ratio, and regenerates a nitrogen oxide trap function of the nitrogen oxide trap catalyst by reducing trapped nitrogen oxides when the excess air factor of the mixture is smaller than the value equivalent to the stoichiometric air-fuel ratio, and the controller is further programmed to determine whether or not a regeneration of the nitrogen oxide trap function is required from the running state, set the target excess air factor to a value larger than the value equivalent to the stoichiometric air-fuel ratio when the regeneration is not required, and set the target excess air factor to a value less than the value equivalent to the stoichiometric air-fuel ratio when the regeneration is required. 12. The excess air factor control device as defined in claim 11, wherein the nitrogen oxide trap catalyst accumulates sulfur in the exhaust gas when the target excess air factor is larger than the value equivalent to the stoichiometric air fuel ratio, and performs a desulphating to release the accumulated sulfur when the target excess air factor is equal to the value equivalent to the stoichiometric air-fuel ratio, and the controller is further programmed to determine whether or not the desulphating is required from the running state, set the target excess air factor to a value larger than the value equivalent to the stoichiometric air-fuel ratio when the desulphating is not required, and set the target excess air factor substantially equal to the value equivalent to the stoichiometric air-fuel ratio when the desulphating is required. 13. The excess air factor control device as defined in claim 3, wherein the diesel engine comprises a particulate filter which traps a particulate matter in the exhaust gas and burns the trapped particulate matter under a predetermined lean air-fuel ratio, and the controller is further programmed to determine whether or not the trapped particulate matter is required to be burned, set the target excess air factor to a first value larger than the value equivalent to the stoichiometric air-fuel ratio when the trapped particulate matter is not required to be burned and set the target excess air factor to a second value which is larger than the value equivalent to the stoichiometric air-fuel ratio but less than the first value when the trapped particulate matter is required to be burned. 14. The excess air factor control device as defined in claim 13, wherein the controller is further programmed to determine that the trapped particulate matter is required to be burned when desulphating is required and set the target excess air factor to the second value after the diesel engine is operated with the target excess air factor substantially equal to the value equivalent to the stoichiometric air-fuel ratio. 15. The excess air factor control device as defined in claim 3, wherein the fuel supply mechanism comprises a fuel injector which injects fuel into the diesel engine, and the controller is further programmed to control a fuel injection timing of the fuel injector to a target injection timing and vary the target injection timing depending on whether or not the target excess air factor is larger than the value equivalent to the stoichiometric air-fuel ratio. 16. The excess air factor control device as defined in claim 15, wherein the controller is further programmed to apply delay processing to the target injection timing when the target excess air factor varies between a value larger than the value equivalent to the stoichiometric air-fuel ratio and a value which is not larger than the value equivalent to the stoichiometric air fuel ratio. 17. An excess air factor control device for a diesel engine which burns a mixture of air supplied by an air supply mechanism and fuel supplied by a fuel supply mechanism, comprising: a sensor which detects a running state of the diesel engine; and a programmable controller programmed to: set a target excess air factor of the mixture based on the running state; control an air supply amount of the air supply mechanism to a target air supply amount calculated from a predetermined fuel supply amount and the target excess air factor when the target excess air factor is larger than a value equivalent to a stoichiometric air-fuel ratio; and control a fuel supply amount of the fuel supply mechanism to a target fuel supply amount calculated from a predetermined air supply amount and the target excess air factor when the target excess air factor is smaller than the value equivalent to the stoichiometric air-fuel ratio; wherein the running state detecting sensor further comprises a sensor which detects a load of the diesel engine and a sensor which detects a rotation speed of the diesel engine, and the controller is further programmed, when the target excess air factor is larger than the value equivalent to the stoichiometric air-fuel ratio equivalent value, to calculate a target engine torque based on the load of the diesel engine and the rotation speed of the diesel engine, calculate a target air amount basic value based on the target engine torque and the rotation speed of the diesel engine, calculate a conversion coefficient based on the target excess air factor and the rotation speed of the diesel engine, set the predetermined air supply amount equal to a value obtained by multiplying the target air amount basic value by the conversion coefficient, and control the air supply amount of the air supply mechanism to the predetermined air supply amount. 18. The excess air factor control device as defined in claim 17, wherein the controller is further programmed, when the target excess air factor is less than the value equivalent to the stoichiometric air-fuel ratio, to calculate a target engine torque based on the load of the diesel engine and the rotation speed of the diesel engine, set a predetermined fuel supply amount equal to a value calculated based on the target engine torque and the rotation speed of the diesel engine, and control the fuel supply amount of the fuel supply mechanism to the predetermined fuel supply amount. 19. The excess air factor control device as defined in claim 17, wherein the running state detecting sensor comprises the controller which is further programmed to count a running time of the diesel engine. 20. The excess air factor control device as defined in claim 17, wherein the controller is further programmed to apply delay processing to the target excess air factor when the target excess air factor varies between a value larger than the value equivalent to the stoichiometric air-fuel ratio and a value which is not larger than the value equivalent to the stoichiometric air-fuel ratio. 21. The excess air factor control device as defined in claim 17, wherein the air supply mechanism comprises a variable geometry turbocharger, and the controller is further programmed to control the air supply amount by varying a turbocharging pressure of the variable geometry turbocharger. 22. The excess air factor control device as defined in claim 17, wherein the air supply mechanism comprises an exhaust gas recirculation valve which recirculates a part of an exhaust gas of the diesel engine into the air supplied by the air supply mechanism, and the controller is further programmed to control the air supply amount by varying an exhaust gas recirculation amount of the exhaust gas recirculation valve. 23. The excess air factor control device as defined in claim 17, wherein the diesel engine comprises an intake passage, the air supply mechanism comprises an intake throttle provided in the intake passage, and the controller is further programmed to control the air supply amount by varying a throttle opening of the intake throttle. 24. The excess air factor control device as defined in claim 17, wherein the diesel engine comprises a nitrogen oxide trap catalyst which traps nitrogen oxides in an exhaust gas of the diesel engine when an excess air factor of the mixture is larger than the value equivalent to the stoichiometric air-fuel ratio, and regenerates a nitrogen oxide trap function of the nitrogen oxide trap catalyst by reducing trapped nitrogen oxides when the excess air factor of the mixture is smaller than the value equivalent to the stoichiometric air-fuel ratio, and the controller is further programmed to determine whether or not a regeneration of the nitrogen oxide trap function is required from the running state, set the target excess air factor to a value larger than the value equivalent to the stoichiometric air-fuel ratio when the regeneration is not required, and set the target excess air factor to a value less than the value equivalent to the stoichiometric air-fuel ratio when the regeneration is required. 25. The excess air factor control device as defined in claim 24, wherein the nitrogen oxide trap catalyst accumulates sulfur in the exhaust gas when the target excess air factor is larger than the value equivalent to the stoichiometric air fuel ratio, and performs a desulphating to release the accumulated sulfur when the target excess air factor is equal to the value equivalent to the stoichiometric air-fuel ratio, and the controller is further programmed to determine whether or not the desulphating is required from the running state, set the target excess air factor to a value larger than the value equivalent to the stoichiometric air-fuel ratio when the desulphating is not required, and set the target excess air factor substantially equal to the value equivalent to the stoichiometric air-fuel ratio when the desulphating is required. 26. The excess air factor control device as defined in claim 17, wherein the diesel engine comprises a particulate filter which traps a particulate matter in the exhaust gas and burns the trapped particulate matter under a predetermined lean air-fuel ratio, and the controller is further programmed to determine whether or not the trapped particulate matter is required to be burned, set the target excess air factor to a first value larger than the value equivalent to the stoichiometric air-fuel ratio when the trapped particulate matter is not required to be burned and set the target excess air factor to a second value which is larger than the value equivalent to the stoichiometric air-fuel ratio but less than the first value when the trapped particulate matter is required to be burned. 27. The excess air factor control device as defined in claim 26, wherein the controller is further programmed to determine that the trapped particulate matter is required to be burned when desulphating is required and set the target excess air factor to the second value after the diesel engine is operated with the target excess air factor substantially equal to the value equivalent to the stoichiometric air-fuel ratio. 28. The excess air factor control device as defined in claim 17, wherein the fuel supply mechanism comprises a fuel injector which injects fuel into the diesel engine, and the controller is further programmed to control a fuel injection timing of the fuel injector to a target injection timing and vary the target injection timing depending on whether or not the target excess air factor is larger than the value equivalent to the stoichiometric air-fuel ratio. 29. The excess air factor control device as defined in claim 28, wherein the controller is further programmed to apply delay processing to the target injection timing when the target excess air factor varies between a value larger than the value equivalent to the stoichiometric air-fuel ratio and a value which is not larger than the value equivalent to the stoichiometric air fuel ratio.