Device for detecting response characteristics of sensor

• US 20050216175A1
• Filed: 03/25/2005
• Published: 09/29/2005
• Est. Priority Date: 03/25/2004
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Yoshiume, Naoki, Morinaga, Shuujirou, Takahashi, Yuri, Iida, Hisashi
• Granted Patent: US 7,103,467 B2
• Time in Patent Office: Days
• US Class Current: 701/109
• CPC Class Codes: F02D 41/1454 the characteristics being an oxygen content or concentration or the air-fuel ratio
• CPC Class Codes: F02D 41/222 relating to the failure of sensors or parameter detection devices
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

When the output of the AFR ratio sensor is stable in a steady operating state, the amount of fuel is increased by step inputting to detect a point where the gradient of change in the sensor output exceeds a threshold value as a point of start of change. The time from the timing of increasing the fuel until the point of start of change is detected as a dead time. A response time is calculated until the amount of change in the sensor output reaches a predetermined ratio of the amount of change (AA−BA) of up to the steady value AA of the sensor output after the amount of the fuel is increased from the steady value BA of the sensor output before the amount of the fuel is increased. The fail condition in the AFR ratio sensor is determined based on the dead time TA and the response time TB.

Claims

1. A device for detecting response characteristics of a sensor applied to an air-fuel ratio control system that controls by feedback the amount of the fuel fed into an internal combustion engine based on an output of a sensor that detects the air-fuel ratio or the oxygen concentration of the exhaust gas emitted from the internal combustion engine, comprising:

fuel changing timing determining means for determining a timing at which the amount of the fuel fed into the internal combustion engine changes; and

step response characteristics detecting means which monitors the behavior of the sensor output before and after the change in the amount of feeding the fuel, and detects the response characteristics of the sensor in a manner of being divided into the dead time from a moment when the amount of feeding the fuel is changed until the sensor output starts changing and the subsequent n-order delay characteristics (n is a positive integer) representing a change in the sensor output.

2. A device for detecting response characteristics of a sensor according to claim 1, further comprising

fail condition determining means for determining the presence of a fail condition in the sensor relying at least upon either the dead time or the n-order delay characteristics detected by the step response characteristics detecting means.

3. A device for detecting response characteristics of a sensor according to claim 1, further comprising

fail condition determining means for determining that the sensor is failed when the processing time exceeds a normal range during the processing of detecting the dead time or the n-order delay characteristics by the step response characteristics detecting means.

4. A device for detecting response characteristics of a sensor according to claim 2, further comprising

normal range setting means for setting a normal range based on at least any one of an operation parameter that affects the response characteristics of the sensor, noise detection data superposed on the output of the sensor, and the operating condition of the internal combustion engine, wherein

the fail condition determining means determines the presence of a fail condition in the sensor relying upon the normal range set by the normal range setting means.

5. A device for detecting response characteristics of a sensor according to claim 2, further comprising

warning means for producing a warning when the fail condition determining means determines that the sensor is failed.

6. A device for detecting response characteristics of a sensor according to claim 1, further comprising

means for changing or correcting an air-fuel ratio feedback control parameter relying at least upon either the dead time or the n-order delay characteristics detected by the step response characteristics detecting means.

7. A device for detecting response characteristics of a sensor according to claim 1, wherein

the step response characteristics detecting means detects the dead time and the n-order delay characteristics by varying the amount of feeding the fuel by step inputting while the internal combustion engine is steady operating near a target air-fuel ratio.

8. A device for detecting response characteristics of a sensor according to claim 1, wherein

the step response characteristics detecting means detects a point (hereinafter referred to as point of start of change) at which the sensor output starts changing after the amount of feeding the fuel has been changed, and detects the time from the timing at which the amount of feeding the fuel is changed until the point of start of change as the dead time.

9. A device for detecting response characteristics of a sensor according to claim 8, wherein

the step response characteristics detecting means detects a point at which a change of gradient in the sensor output exceeds a threshold value after the amount of feeding the fuel has been changed as a point of start of change.

10. A device for detecting response characteristics of a sensor according to claim 9, wherein

the step response characteristics detecting means detects the point of start of change successively until the change of gradient in the sensor output exceeds the threshold value a predetermined number of times after the amount of feeding the fuel has been changed.

11. A device for detecting response characteristics of a sensor according to claim 9, further comprising

threshold value setting means for setting a threshold value based on an operation parameter that affects the noise superposed on the sensor output or based on the noise detection data.

12. A device for detecting response characteristics of a sensor according to claim 1, wherein

the step response characteristics detecting means detects response times of a number of not less than n+1 to estimate a curve of change in the sensor output of the n-order delay, estimates a point (hereinafter referred to as point of start of change) at which the sensor output starts changing after the amount of feeding the fuel has been changed based on the curve of change in the sensor output and the sensor output in a steady state of before the amount of feeding the fuel is changed, and calculates the dead time by using the point of start of change.

13. A device for detecting response characteristics of a sensor according to claim 1, wherein the step response characteristics detecting means includes:

first dead time calculation means which detects a point (hereinafter referred to as point of start of change) at which the sensor output starts changing after the amount of feeding the fuel has been changed, and detects the time from the timing at which the amount of feeding the fuel is changed until the point of start of change as the dead time; and

second dead time calculation means which detects response times of a number of not less than n+1 to estimate a curve of change in the sensor output of the n-order delay, estimates a point of start of change based on the curve of change in the sensor output and on the sensor output in a steady state of before the amount of feeding the fuel is changed, and calculates the dead time by using the point of start of change,

wherein the step response characteristics detecting means calculates the dead time by selecting either one of the first dead time calculation means or the second dead time calculation means depending upon the amount of change in the sensor output of before the amount of feeding the fuel is changed or upon the operating conditions.

14. A device for detecting response characteristics of a sensor according to claim 1, wherein

the step response characteristics detecting means calculates a response time or a coefficient of transfer function of the n-order delay before the amount of change in the sensor output reaches a predetermined ratio at the time of detecting the n-order delay characteristics.

15. A device for detecting response characteristics of a sensor according to claim 14, wherein

the step response characteristics detecting means calculates the amount of change in the sensor output at the time of detecting the n-order delay characteristics based on the steady state of before the amount of feeding the fuel is changed, and calculates a response time until the amount of change reaches a predetermined ratio of the amount of change of up to the steady state of after the amount of feeding the fuel is changed from the steady state of before the amount of feeding the fuel is changed.

16. A device for detecting response characteristics of a sensor according to claim 14, wherein in detecting the n-order delay characteristics, the step response characteristics detecting means detects the response times of a number of not less than n+1, and calculates the coefficient of transfer function that represents the response of the n-order delay based on the response times of the number of not less than n+1.

17. A device for detecting response characteristics of a sensor according to claim 2, wherein

the step response characteristics detecting means detects the response characteristics of the sensor under a predetermined operating condition, and estimates the response characteristics under other operating conditions based on the detected value thereof.

18. A device for detecting response characteristics of a sensor according to claim 2, wherein

the fail condition determining means determines the presence of a fail condition in the sensor when the output of the sensor has changed from rich to lean and from lean to rich, respectively.