Control device and control method for internal combustion engine

1. A control device for an internal combustion engine including an upstream cleaning device and a downstream cleaning device that are provided in an exhaust gas passage and a temperature sensor configured to detect a temperature of exhaust gas between the upstream cleaning device and the downstream cleaning device, the control device comprising:

a processor configured to

estimate a temperature of the downstream cleaning device without using the temperature of exhaust gas detected by the temperature sensor;

estimate a temperature of the upstream cleaning device without using the temperature of exhaust gas detected by the temperature sensor; and

in response to (i) the estimated temperature of the upstream cleaning device being equal to or higher than a predetermined first lower-limit temperature and (ii) the estimated temperature of the downstream cleaning device being equal to or higher than a predetermined second lower-limit temperature, perform an abnormality determining process for the upstream cleaning device,

wherein the processor is configured to estimate the temperature of the downstream cleaning device and the temperature of the upstream cleaning device based on a temperature of exhaust gas flowing out of an exhaust port of the internal combustion engine, an amount of heat transmitted between exhaust gas and an exhaust pipe, and an amount of heat discharged from the exhaust pipe.

2. The control device according to claim 1 ,

wherein the internal combustion engine further includes

a supercharger including (i) a turbine wheel that is provided in the exhaust gas passage and (ii) a compressor wheel that is connected to the turbine wheel via a turbine shaft and provided in an intake air passage of the internal combustion engine, and

wherein the processor is configured to

estimate the temperature of the upstream cleaning device based on

a temperature of exhaust gas flowing out of the turbine wheel estimated based on the temperature of exhaust gas flowing out of the exhaust port,

an amount of heat transmitted between exhaust gas and the exhaust pipe from the turbine wheel to the upstream cleaning device, and

the amount of heat discharged from the exhaust pipe and

estimate the temperature of the downstream cleaning device based on

the estimated temperature of the upstream cleaning device,

an amount of heat transmitted between exhaust gas and the exhaust pipe from the upstream cleaning device to the downstream cleaning device, and

the amount of heat discharged from the exhaust pipe.

3. The control device according to claim 1 ,

wherein the internal combustion engine further includes an air-fuel ratio sensor that detects an air-fuel ratio of exhaust gas between the upstream cleaning device and the downstream cleaning device,

wherein the abnormality determining process is active air-fuel ratio control for forcibly and alternately switching an air-fuel ratio of exhaust gas flowing into the upstream cleaning device to a rich side or a lean side with change of the air-fuel ratio detected by the air-fuel ratio sensor to the lean side or the rich side, and

wherein the processor is further configured to

estimate an amount of oxygen stored and an amount of oxygen discharged by the upstream cleaning device while the active air-fuel ratio control is being performed, and

determine whether an abnormality in the upstream cleaning device occurs based on the estimated amount of stored oxygen and the estimated amount of discharged oxygen.

4. The control device according to claim 1 ,

wherein the upstream cleaning device includes a three-way catalyst,

wherein the downstream cleaning device includes a particulate filter, and

wherein the processor is further configured to

estimate a temperature of the downstream cleaning device from the temperature of exhaust gas detected by the temperature sensor, and

determine whether supply of fuel for regenerating the downstream cleaning device is to be stopped based on the temperature estimated from the temperature of exhaust gas detected by the temperature sensor.

5. A control method for an internal combustion engine including an upstream cleaning device and a downstream cleaning device that are provided in an exhaust gas passage and a temperature sensor that detects a temperature of exhaust gas between the upstream cleaning device and the downstream cleaning device, the control method comprising:

estimating a temperature of the downstream cleaning device without using the temperature of exhaust gas detected by the temperature sensor;

estimating a temperature of the upstream cleaning device without using the temperature of exhaust gas detected by the temperature sensor; and

in response to (i) the estimated temperature of the upstream cleaning device being equal to or higher than a predetermined first lower-limit temperature and (ii) the estimated temperature of the downstream cleaning device being equal to or higher than a predetermined second lower-limit temperature, performing an abnormality determining process for the upstream cleaning device,

wherein the temperature of the downstream cleaning device and the temperature of the upstream cleaning device are estimated based on a temperature of exhaust gas flowing out of an exhaust port of the internal combustion engine, an amount of heat transmitted between exhaust gas and an exhaust pipe, and an amount of heat discharged from the exhaust pipe.