Exhaust purification system of internal combustion engine

Patent metadata

Field	Value
Publication number	US-9835104-B2
Application number	US-201615083449-A
Country	US
Kind code	B2
Filing date	Mar 29, 2016
Priority date	Mar 31, 2015
Publication date	Dec 5, 2017
Grant date	Dec 5, 2017

Abstract

An exhaust purification system comprising an exhaust purification catalyst, a downstream side air-fuel ratio sensor, and a control device performing air-fuel ratio control for controlling an air-fuel ratio of exhaust gas and abnormality diagnosis control for diagnosing the downstream side air-fuel ratio sensor. In the air-fuel ratio control, the control device alternately and repeatedly switches the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst between a rich air-fuel ratio and a lean air-fuel ratio. In the abnormality diagnosis control, the control device judges that the downstream side air-fuel ratio sensor has become abnormal when the air-fuel ratio of the exhaust gas is made the rich air-fuel ratio by the air-fuel control and the output air-fuel ratio of the downstream side air-fuel ratio sensor changes from an air-fuel ratio richer than a predetermined lean judged air-fuel ratio to an lean air-fuel ratio.

First claim

The invention claimed is:

1. An exhaust purification system of an internal combustion engine, the exhaust purification system comprising:
an exhaust purification catalyst provided in an exhaust passage of the internal combustion engine, a downstream side air-fuel ratio sensor provided in the exhaust passage at a downstream side of the exhaust purification catalyst in a direction of flow of exhaust, and a control device performing air-fuel ratio control for controlling an air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst and abnormality diagnosis control for diagnosing the downstream side air-fuel ratio sensor for abnormality based on an output air-fuel ratio of the downstream side air-fuel ratio sensor, wherein,
in the air-fuel ratio control, the control device alternately and repeatedly switches the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst between a rich air-fuel ratio richer than a stoichiometric air-fuel ratio and a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio, and,
in the abnormality diagnosis control, the control device judges that the downstream side air-fuel ratio sensor has become abnormal when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is made the rich air-fuel ratio by the air-fuel ratio control and the output air-fuel ratio of the downstream side air-fuel ratio sensor changes from an air-fuel ratio richer than a predetermined lean judged air-fuel ratio leaner than the stoichiometric air-fuel ratio to an air-fuel ratio leaner than the predetermined lean judged air-fuel ratio.

2. The exhaust purification system of an internal combustion engine according to claim 1 , wherein
in the air-fuel ratio control, the control device further performs feedback control of an amount of fuel fed to a combustion chamber of the internal combustion engine so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes a target air-fuel ratio, and learning control correcting a parameter relating to the air-fuel ratio based on the output air-fuel ratio of the downstream side air-fuel ratio sensor,
in the air-fuel control, the control device alternately switches the target air-fuel ratio between a rich air-fuel ratio and a lean air-fuel ratio and, when the output air-fuel ratio of the downstream side air-fuel ratio sensor becomes equal to or less than a predetermined rich judged air-fuel ratio that is richer than the stoichiometric air-fuel ratio, switches the target air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio,
in the learning control, the control device corrects a parameter relating to the air-fuel ratio based on a cumulative oxygen excess amount, which is a cumulative value of an amount of oxygen becoming in excess when making the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst the stoichiometric air-fuel ratio in an oxygen increase time period from when switching the target air-fuel ratio to the lean air-fuel ratio to when again switching the target air-fuel ratio to the rich air-fuel ratio, and a cumulative oxygen deficiency amount, which is a cumulative value of an amount of oxygen becoming deficient when making the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst the stoichiometric air-fuel ratio in an oxygen decrease time period from when switching the target air-fuel ratio to the rich air-fuel ratio to when again switching the target air-fuel ratio to the lean air-fuel ratio, so that the control device reduces a difference between the cumulative oxygen excess amount and the cumulative oxygen deficiency amount and,
if judging that the downstream side air-fuel ratio sensor has become abnormal when the target air-fuel ratio is set to the rich air-fuel ratio, the control device stops correction of the parameter relating to the air-fuel ratio based on the cumulative oxygen deficiency amount at this time even if after that the output air-fuel ratio of the downstream side air-fuel ratio sensor becomes less than or equal to the predetermined rich judged air-fuel ratio and the target air-fuel ratio is switched to the lean air-fuel ratio.

3. The exhaust purification system of an internal combustion engine according to claim 2 , wherein, when the target air-fuel ratio is set to the rich air-fuel ratio, the output air-fuel ratio of the downstream side air-fuel ratio sensor changes from an air-fuel ratio richer than the predetermined lean judged air-fuel ratio to an air-fuel ratio leaner than the predetermined lean judged air-fuel ratio, and thereby it is judged that the downstream side air-fuel ratio sensor has become abnormal, the control device calculates the cumulative oxygen deficiency amount in a time period from when switching the target air-fuel ratio to the rich air-fuel ratio a last time to when the output air-fuel ratio of the downstream side air-fuel ratio sensor changes from an air-fuel ratio richer than the predetermined lean judged air-fuel ratio to an air-fuel ratio leaner than the predetermined lean judged air-fuel ratio, and corrects the parameter relating to the air-fuel ratio so that the control device reduces the difference between the cumulative oxygen deficiency amount and the cumulative oxygen excess amount.

4. The exhaust purification system of an internal combustion engine according to claim 3 , wherein,
in the air-fuel ratio control, the control device alternately switches the target air-fuel ratio between a constant rich set air-fuel ratio richer than the stoichiometric air-fuel ratio and a constant lean set air-fuel ratio leaner than the stoichiometric air-fuel ratio, and
the control device reduces a rich degree of the rich set air-fuel ratio if judging that the downstream side air-fuel ratio sensor has become abnormal by the abnormal diagnosis control.

5. The exhaust purification system of an internal combustion engine according to claim 4 , wherein,
in the air-fuel ratio control, if defining a time period setting the target air-fuel ratio to the rich air-fuel ratio and lean air-fuel ratio one time each as one cycle,
the control device reduces the rich degree of the rich set air-fuel ratio if, during a given number of cycles, a ratio of a number of times the downstream side air-fuel ratio sensor is judged to be abnormal to the given number of cycles is greater than or equal to a predetermined value.

6. The exhaust purification system of an internal combustion engine according to claim 5 , wherein,
in the air-fuel ratio control, the control device switches the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst from the rich air-fuel ratio to the lean air-fuel ratio when the output air-fuel ratio of the downstream side air-fuel ratio sensor becomes equal to or less than a predetermined rich judged air-fuel ratio richer than the stoichiometric air-fuel ratio, and switches the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst from the lean air-fuel ratio to the rich air-fuel ratio when an oxygen storage amount of the exhaust purification catalyst becomes greater than or equal to a predetermined switching reference oxygen amount, said predetermined switching reference oxygen amount being less than a maximum storable oxygen amount.

7. The exhaust purification system of an internal combustion engine according to claim 4 , wherein,
in the air-fuel ratio control, the control device switches the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst from the rich air-fuel ratio to the lean air-fuel ratio when the output air-fuel ratio of the downstream side air-fuel ratio sensor becomes equal to or less than a predetermined rich judged air

Assignees

• Toyota Motor Co Ltd

Inventors

• Okazaki Shuntaro
• Suzuki Kenji
• Miyamoto Hiroshi
• Miyoshi Yuji

Classifications

• F01N2900/0416

  using the state of a sensor, e.g. of an exhaust gas sensor · CPC title

• F02D41/1475

  Regulating the air fuel ratio at a value other than stoichiometry · CPC title

• F02D2200/0814

  Oxygen storage amount · CPC title

• F02D41/1456

  with sensor output signal being linear or quasi-linear with the concentration of oxygen · CPC title

• F02D41/2454

  Learning of the air-fuel ratio control · CPC title