Control device and control method for an internal combustion engine

1. A control method which controls an internal combustion engine, comprising:

determining, based on an operation amount of an accelerator operated by a driver and an rpm of the internal combustion engine, whether an operation range requested by the driver is a supercharging operation range or a non-supercharging operation range;

determining whether a ratio of the pressure of an intake manifold and an atmospheric pressure is smaller than a threshold value when the operation range is the non-supercharging operation range;

calculating a target opening degree of a wastegate valve provided in a bypass passage of an exhaust passage, based on the ratio of the pressure of the intake manifold and the atmospheric pressure; and

adjusting an opening degree of the wastegate valve based on the calculated target opening degree,

wherein the calculating, as a full-closure value, the target opening degree of the wastegate valve when the ratio of the pressure of the intake manifold and the atmospheric pressure is smaller than the threshold value.

2. A control device which controls an internal combustion engine comprising:

a non-transitory computer readable medium having software code stored thereon to execute operations of:

determining whether an operation range requested by the driver is a supercharging operation range or a non-supercharging operation range based on an operation amount of an accelerator by a driver and an rpm of the internal combustion engine;

determining whether a ratio of a pressure of an intake manifold and an atmospheric pressure is smaller than a threshold value when the operation range is the non-supercharging operation range;

calculating a target opening degree of a wastegate valve provided in a bypass passage of an exhaust passage, based on the determined ratio of the pressure of the intake manifold and the atmospheric pressure; and

adjusting an opening degree of the wastegate valve based on the target opening degree,

wherein the calculating comprises calculating-, as a full-closure value, the target opening degree of the wastegate valve when the ratio of the pressure of the intake manifold and the atmospheric pressure is smaller than the threshold value.

3. The control device for an internal combustion engine according to claim 2 , wherein the internal combustion engine comprises a throttle upstream pressure sensor configured to detect a pressure upstream of a throttle valve provided in an intake passage of the internal combustion engine, and

the throttle upstream pressure sensor being provided in the intake passage located between a supercharger and the throttle valve; and

wherein the non-supercharging operation range includes a first region in which the wastegate valve is allowed to be fully closed and a second region in which the wastegate valve is not allowed to be fully closed; and

wherein the operations further comprise setting the target opening degree of the wastegate valve to fully close the wastegate valve in the first region and setting the target opening degree of the wastegate valve to a value which allows the wastegate valve to be closed by a predetermined amount so that the ratio of the pressure upstream of the throttle valve provided in an intake passage of the internal combustion engine and the atmospheric pressure does not exceed a threshold value in the second region.

4. The control device for an internal combustion engine according to claim 3 , wherein the operations further comprise based on the operation amount of the accelerator and the rpm of the internal combustion engine, determining whether or not deceleration/fuel-cut processing is being performed,

wherein the setting comprises setting the opening degree of the wastegate valve to fully close the wastegate valve regardless of the ratio of the pressure of the intake manifold and the atmospheric pressure when the deceleration/fuel-cut processing is being performed.

5. The control device for an internal combustion engine according to claim 2 , wherein the operations further comprise determining, based on the operation amount of the accelerator and the rpm of the internal combustion engine, whether or not deceleration/fuel-cut processing is being performed,

wherein the calculating comprises setting the opening degree of the wastegate valve to fully close the wastegate valve regardless of the ratio of the pressure of the intake manifold and the atmospheric pressure when the deceleration/fuel-cut processing is being performed.

6. A control device for an internal combustion engine, which comprises:

a throttle valve provided in an intake passage of the internal combustion engine;

a supercharger including a turbine provided in an exhaust passage of the internal combustion engine and a compressor provided upstream of the throttle valve in the intake passage, the compressor being configured to rotate integrally with the turbine;

a wastegate valve provided in a bypass passage, the bypass passage being provided to the exhaust passage so as to bypass the turbine;

an intake-manifold pressure sensor detecting a pressure of an intake manifold provided downstream of the throttle valve;

an atmospheric-pressure sensor detecting an atmospheric pressure outside of the internal combustion engine;

an accelerator position sensor detecting an operation amount of an accelerator by a driver; and

an rpm sensor for detecting an rpm of the internal combustion engine,

the control device having software stored on a non-transitory computer readable medium to execute operations of:

determining whether an operation range requested by the driver is a supercharging operation range or a non-supercharging operation range based on the operation amount of the accelerator and the rpm of the internal combustion engine as previously detected;

determining whether a ratio of the pressure of the intake manifold and the atmospheric pressure as previously detected is smaller than a threshold value when the operation range is the non-supercharging operation range;

determining a target opening degree of the wastegate valve based on the ratio of the pressure of the intake manifold and the atmospheric pressure as previously detected, wherein the target opening degree of the wastegate valve is equal to a full-closure value when the ratio of the pressure of the intake manifold an the atmospheric pressure as previously detected is smaller than the threshold value; and

actuating the wastegate valve by a wastegate actuator to adjust an opening degree of the wastegate valve as previously detected and changing a flow-path sectional area of the by-pass passage based on the target opening degree as previously determined.

7. The control device for an internal combustion engine according to claim 6 , wherein the internal combustion engine comprises a throttle upstream pressure sensor configured to detect a pressure upstream of a throttle valve, and the throttle upstream pressure sensor being provided in the intake passage located between a supercharger and the throttle valve;

wherein the non-supercharging operation range includes a first region in which the wastegate valve is allowed to be fully closed and a second region in which the wastegate valve is not allowed to be fully closed; and

wherein the control devices has the software to further execute an operation of setting the target opening degree of the wastegate valve to fully close the wastegate valve in the first region and setting the target opening degree of the wastegate valve to a value which allows the wastegate valve to be closed by a predetermined amount so that the ratio of the pressure upstream of the throttle valve provided in an intake passage of the internal combustion engine and the atmospheric pressure does not exceed a threshold value in the second region.

8. The control device for an internal combustion engine according to claim 6 , wherein the control device has the software to further execute the operations of:

determining, based on the operation amount of the accelerator and the rpm of the internal combustion engine, whether or not deceleration/fuel-cut processing is being performed, and

setting the opening degree of the wastegate valve to fully close the wastegate valve regardless of the ratio of the pressure of the intake manifold and the atmospheric pressure when the deceleration/fuel-cut processing is being performed.

9. The control device for an internal combustion engine according to claim 7 , wherein the control device has the software to further execute the operations of:

determining, based on the operation amount of the accelerator and the rpm of the internal combustion engine, whether or not deceleration/fuel-cut processing is being performed, and

setting the opening degree of the wastegate valve to fully close the wastegate valve regardless of the ratio of the pressure of the intake manifold and the atmospheric pressure when the deceleration/fuel-cut processing is being performed.

10. An internal combustion engine system, which comprises:

an internal combustion engine comprising:

a throttle valve provided in an intake passage of the internal combustion engine; a supercharger including a turbine provided in an exhaust passage of the internal combustion engine and a compressor provided upstream of the throttle valve in the intake passage, the compressor being configured to rotate integrally with the turbine;

a wastegate valve provided in a bypass passage, the bypass passage being provided to the exhaust passage so as to bypass the turbine;

an intake-manifold pressure sensor detecting a pressure of an intake manifold provided downstream of the throttle valve;

an atmospheric-pressure sensor detecting an atmospheric pressure outside of the internal combustion engine;

an accelerator position sensor detecting an operation amount of an accelerator by a driver; and

an rpm sensor for detecting an rpm of the internal combustion engine; and

a control device having software stored on a non-transitory computer readable medium to execute operations of:

determining whether an operation range requested by the driver is a supercharging operation range or a non-supercharging operation range based on the operation amount of the accelerator and the rpm of the internal combustion engine as previously detected;

determining whether a ratio of the pressure of the intake manifold and the atmospheric pressure as previously detected is smaller than a threshold value when the operation range is the non-supercharging operation range;

determining a target opening degree of the wastegate valve based on the ratio of the pressure of the intake manifold and the atmospheric pressure as previously detected, wherein the target opening degree of the wastegate valve is equal to a full-closure value when the ratio of the pressure of the intake manifold an the atmospheric pressure as previously detected is smaller than the threshold value; and

actuating the wastegate valve by a wastegate actuator to adjust an opening degree of the wastegate valve as previously detected and changing a flow-path sectional area of the by-pass passage based on the target opening degree as previously determined.