EGR SYSTEM FOR INTERNAL COMBUSTION ENGINE AND METHOD FOR CONTROLLING THE SAME

Abstract:

An EGR system includes a high-pressure EGR passage that provides communication between an exhaust pipe, at a portion upstream of a turbine of a turbocharger, and an intake pipe, at a portion downstream of a compressor; a low-pressure EGR passage that provides communication between the exhaust pipe, at a portion downstream of the turbine, and the intake passage, at a portion upstream of the compressor; and an exhaust gas catalyst provided upstream of a position at which the low-pressure EGR passage is connected to the exhaust pipe. When an internal combustion engine is in the transitional state from the low-load operating state to the high-load operating state (S303), if incomplete combustion is detected in the internal combustion engine (S304) and the bed temperature of the exhaust gas catalyst is lower than the reference temperature (S305), the high-pressure EGR gas amount is made larger than the prescribed high-pressure EGR gas amount determined based on the operating state of the internal combustion engine (S306). Thus, an excessive decrease in the intake air temperature is suppressed, and therefore occurrence of incomplete combustion is suppressed.
Claims:
1. An EGR system for an internal combustion engine, comprising:a turbocharger that has a compressor in an intake passage of the internal combustion engine, and that has a turbine in an exhaust passage of the internal combustion engine;a high-pressure EGR unit that recirculates a portion of exhaust gas back to the internal combustion engine through a high-pressure EGR passage that provides communication between the exhaust passage, at a portion upstream of the turbine, and the intake passage, at a portion downstream of the compressor;a low-pressure EGR unit that recirculates a portion of the exhaust gas back to the internal combustion engine through a low-pressure EGR passage that provides communication between the exhaust passage, at a portion downstream of the turbine, and the intake passage, at a portion upstream of the compressor; andan EGR control unit that controls the high-pressure EGR unit and the low-pressure EGR unit such that a high-pressure EGR gas amount which is an amount of high-pressure EGR gas recirculated back to the internal combustion engine by the high-pressure EGR unit and a low-pressure EGR gas amount which is an amount of low-pressure EGR gas recirculated back to the internal combustion engine by the low-pressure EGR unit match a prescribed high-pressure EGR gas amount and a prescribed low-pressure EGR gas amount, respectively, based on an operating state of the internal combustion engine,wherein the EGR control unit increases a ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount, when the internal combustion engine is in a transitional state from a low-load operating state to a high-load operating state,wherein the EGR control unit makes the high-pressure EGR gas amount larger than the prescribed high-pressure EGR gas amount, when the internal combustion engine is in the transitional state from the low-load operating state to the high-load operating state, andwherein the EGR control until sets the ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount higher in the low-load operating state than in the high-load operating state.

2. The EGR system according to claim 1, wherein the EGR control unit makes the low-pressure EGR gas amount smaller than the prescribed low-pressure EGR gas amount, when the internal combustion engine is in the transitional state from the low-load operating state to the high-load operating state.

3. The EGR system according to claim 1, further comprising:a combustion state detection unit that detects a fuel combustion state in the internal combustion engine,whereinthe EGR control unit increases the ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount, if incomplete fuel combustion is detected by the combustion state detection unit when the internal combustion engine is in the transitional state from the low-load operating state to the high-load operating state.

4. The EGR system according to claim 3, further comprising:a catalyst temperature detection unit that estimates or detects a temperature of an exhaust gas catalyst which is provided upstream of a portion at which the low-pressure EGR passage is connected to the exhaust passage,whereinthe EGR control unit increases the ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount, if incomplete fuel combustion is detected by the combustion state detection unit and the temperature of the exhaust gas catalyst estimated or detected by the catalyst temperature detection unit is lower than a predetermined temperature, when the internal combustion engine is in the transitional state from the low-load operating state to the high-load operating state.

5. The EGR system according to claim 4, wherein the EGR control unit resets the high-pressure EGR gas amount and the low-pressure EGR gas amount to the prescribed high-pressure EGR gas amount and the prescribed low-pressure EGR gas amount, respectively, when the temperature of the exhaust gas catalyst estimated or detected by the catalyst temperature detection unit exceeds the predetermined temperature.

6. The EGR system according to claim 1, wherein the EGR control unit resets the high-pressure EGR gas amount and the low-pressure EGR gas amount to the prescribed high-pressure EGR gas amount and the prescribed low-pressure EGR gas amount, respectively, when a predetermined time has elapsed since a control for increasing the ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount is executed.

7. A method for controlling an EGR system for an internal combustion engine, the EGR system including a turbocharger that has a compressor in an intake passage of the internal combustion engine, and that has a turbine in an exhaust passage of the internal combustion engine, comprising:recirculating a portion of exhaust gas back to the internal combustion engine through a high-pressure EGR passage that provides communication between the exhaust passage, at a portion upstream of the turbine, and the intake passage, at a portion downstream of the compressor;recirculating a portion of the exhaust gas back to the internal combustion engine through a low-pressure EGR passage that provides communication between the exhaust passage, at a portion downstream of the turbine, and the intake passage, at a portion upstream of the compressor;executing a control such that a high-pressure EGR gas amount which is an amount of high-pressure EGR gas recirculated back to the internal combustion engine and a low-pressure EGR gas amount which is an amount of low-pressure EGR gas recirculated back to the internal combustion engine match a prescribed high-pressure EGR gas amount and a prescribed low-pressure EGR gas amount, respectively, based on an operating state of the internal combustion engine;increasing a ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount, when the internal combustion engine is in a transitional state from a low-load operating state to a high-load operating state;increasing the ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount by making the high-pressure EGR gas amount larger than the prescribed high-pressure EGR gas amount, when the internal combustion engine is in the transitional state from the low-load operating state to the high-load operating state; andsetting the ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount higher in the low-load operating state than in the high-load operating state.

8. The method according to claim 7, wherein the ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount is increased by making the low-pressure EGR gas amount smaller than the prescribed low-pressure EGR gas amount, when the internal combustion engine is in the transitional state from the low-load operating state to the high-load operating state.

9. The method according to claim 7, further comprising:detecting a fuel combustion state in the internal combustion engine,whereinthe ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount is increased, if incomplete fuel combustion is detected when the internal combustion engine is in the transitional state from the low-load operating state to the high-load operating state.

10. The method according to claim 9, further comprising:estimating or detecting a temperature of an exhaust gas catalyst which is provided upstream of a portion at which the low-pressure EGR passage is connected to the exhaust passage,whereinthe ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount is increased, if incomplete fuel combustion is detected and the temperature of the estimated or detected exhaust gas catalyst is lower than a predetermined temperature, when the internal combustion engine is in the transitional state from the low-load operating state to the high-load operating state.

11. The method according to claim 10, wherein the high-pressure EGR gas amount and the low-pressure EGR gas amount are reset to the prescribed high-pressure EGR gas amount and the prescribed low-pressure EGR gas amount, respectively, when the estimated or detected temperature of the exhaust gas catalyst exceeds the predetermined temperature.

12. The method according to claim 7, wherein the high-pressure EGR gas amount and the low-pressure EGR gas amount are reset to the prescribed high-pressure EGR gas amount and the prescribed low-pressure EGR gas amount, respectively, when a predetermined time has elapsed since a control for increasing the ratio of the high-pressure EGR gas amount to the low-pressure EGR gas amount is executed

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