CLIAMS:We Claim:
1 A method to initialize monitoring of an error in an exhaust gas recirculation (EGR) system, the method comprising:
monitoring an engine shut-off event;
sensing an engine start event; and
initializing monitoring of said error in dependence of said engine start event.

2 The method as claimed in claim 1, wherein said engine start event is sensed after a pre-determined time period.

3 A method of monitoring an error in an exhaust gas recirculation (EGR) system, the method comprising:
sensing an engine start event;
recording a temperature value of exhaust gases;
monitoring real time temperature value of said exhaust gases;
calculating difference between recorded temperature value and said real time temperature value;
comparing said difference with a temperature threshold value to determine an error; and
indicating said error in dependence of said comparison.

4 The method as claimed in claim 1, wherein said engine start event is sensed after a pre-determined time period.

5 The method as claimed in claim 1, wherein said temperature threshold value is a low threshold value.

6 The method as claimed in claim 1, wherein said temperature threshold value is a high threshold value.

7 The method as claimed in claim 1, wherein said error is a low flow error.

8 The method as claimed in claim 1, wherein said error is a high flow error.

9 The method as claimed in claim 1, wherein said error is indicated using an audio indicator.

10 The method as claimed in claim 1, wherein said error is indicated using a visual indicator. ,TagSPECI:Field of the invention
[001] This invention relates to the field Exhaust gas recirculation (EGR) system, and more specifically to the field of monitoring a high flow error and a low flow error of exhaust gases in the EGR system.

Background of the invention
[002] Exhaust gas recirculation (EGR) in which exhaust gases are recirculated back into an intake passage of an engine is a known method for reducing Nox emission in the exhaust gases. An EGR system comprises an EGR valve along with a feedback sensor used for recirculation of the exhaust gases.

[003] Position of the EGR valve is varied to control supply of the exhaust gases for recirculation. Sometimes position of the EGR valve is such that the exhaust gases recirculated may be higher than the appropriate amount of the exhaust gases required for recirculation. This condition is referred to as EGR high flow error. In few other cases the position of the EGR valve is such that the amount of exhaust gases recirculated may be lesser than the appropriate amount of the exhaust gases required for recirculation. This condition is referred to as EGR low flow error.

[004] The feedback sensor is used to correct the EGR valve position such that appropriate amount of exhaust gases are supplied for recirculation. If the EGR valve position is stuck between an open position and a close position, an electronic control unit may report an EGR high flow error or an EGR low flow error respectively. However, the electronic control unit fails to identify an error in the EGR system during other instances, for example when there is a blockage in the EGR passage. In such cases a technique to monitor the EGR system is required. An US patent number 4,793, 318 discloses one such method of monitoring the EGR system to solve this problem.

Brief description of the accompanying drawings

[005] Figure. 1 illustrates a block diagram representing a method to initialize monitoring of an error in an exhaust gas recirculation (EGR) system; and

[006] Figure. 2 illustrates a block diagram representing a method of monitoring an error in an exhaust gas recirculation (EGR) system.

Detailed description

[007] Figure. 1 illustrates a block diagram representing a method to initialize monitoring of an error in an exhaust gas recirculation (EGR) system. In accordance with this invention, the method includes the following steps: Monitoring an engine shut-off event represented as step 105, sensing an engine start event represented as step 110 and initializing monitoring of an error in dependence of the engine start event represented as step 115. The error may be a high flow error and low flow error. The method of initializing is performed to ensure that no additional source of heat is included during monitoring of the EGR system.

[008] Figure. 2 illustrates a block diagram representing a method of monitoring an error in the EGR system. In accordance with this invention, the method includes the following steps: Sensing an engine start event represented as step 205. Recording a temperature value of exhaust gases represented as step 210. The temperature value represents appropriate amount of the exhaust gases required for the EGR system. Monitoring real time temperature value of the exhaust gases represented as step 215. Calculating difference between recorded temperature value and the real time temperature value represented as step 220. Comparing the difference with a temperature threshold value to determine an error represented as step 225 and indicating the error in dependence of said comparison represented as step 230.

[009] An electronic control unit is adapted to perform a method of initializing the monitoring of of an error in the EGR system. The electronic control unit is configured to monitor an engine shut-off event. An engine off timer may be used for this purpose. The electronic control unit is also configured to sense an engine start. The engine start event is determined after a pre-determined time period. In one example, the pre-determined time period may be a duration of six hours. The electronic control unit may receive an electrical signal from the engine off timer once the engine begins to run after the pre-determined time period. Sensing of the engine start event after a pre-determined time period is performed to ensure that temperature of the engine is identical with environmental temperature and that no other source of heat is contributing to monitoring process.

[0010] In some embodiments, in order to ensure that no other heat source intercedes during the monitoring process, temperature values of a plurality of sensors may be sensed to check if the temperature values are identical with respect to each other. The electronic control unit may be adapted to receive temperature values from the sensors and further compares such temperature values with each other to determine if such temperature values are similar to each other.

[0011] Upon sensing the engine start event, the electronic control unit is further adapted to record the temperature value of the exhaust gases. The temperature value of the exhaust gases represent appropriate amount of exhaust gases required for recirculation in the EGR system to meet the on board diagnostic (OBD) requirements of the EGR system.

[0012] The temperature value of the exhaust gases is computed based on a plurality of factors such as an EGR valve position, an engine speed, coolant temperature, fuel injection quantity and atmospheric pressure.

[0013] The temperature value of the exhaust gases is recorded using the following steps: Amount of exhaust gases, flowing in the EGR system, is determined based on the engine speed and the fuel injection quantity with respect to standard engine testing conditions provided by a legislation authority. A calibration map may be used to determine the amount of exhaust gases, flowing in the EGR system, based on the engine speed and the fuel injection quantity.

[0014] Also, the amount of exhaust gases, flowing in the EGR system, is determined based on the coolant temperature and the atmospheric pressure.

[0015] Further, total amount of exhaust gases, flowing in the EGR system, is calculated by addition of the determined amount of exhaust gases based on the engine speed and the fuel injection quantity and the determined amount of exhaust gases based on the coolant temperature and the atmospheric pressure.

[0016] Furthermore, the temperature value is recorded using the determined total amount of exhaust gases and the EGR valve position. A lookup table or a map may be used to record the temperature value. The temperature value thus recorded represents appropriate amount of exhaust gases required for recirculation in the EGR system to meet the OBD requirements of the EGR system.

[0017] Upon recording the temperature value, the electronic control unit is adapted to monitor the real time temperature value of the exhaust gases. A temperature sensor located downstream of the EGR valve is used to measure the real time temperature value of the exhaust gases. The real time temperature value represents the amount of exhaust gases flowing in the exhaust path in real time once the engine is running after the pre-determined time.

[0018] Further, the electronic control unit is configured to calculate difference between the recorded temperature value and the real time temperature value monitored by the temperature sensor.
[0019] Furthermore the electronic control unit is adapted to compare the difference with a temperature threshold value to determine an error. In one instance, the temperature threshold value is a low threshold value. In another instance, the temperature threshold value is a high threshold value. The high threshold value and the low threshold value are pre-calibrated values based on specification of the engine.

[0020] The error includes either a low flow error or a high flow error. If value of the difference calculated is lesser than the low threshold value then the error is considered to be a low flow error. Low flow error indicates that the exhaust gases flowing in the EGR system is inadequate and consequently may result in higher Nox emissions. Further, if value of the difference calculated is higher than the high threshold value then the error is considered to be a high flow error. The high flow error indicates that the exhaust gases flowing in the EGR system is in excess and consequently may result in higher emission of particulate matter.

[0021] On detection of the low flow error or high flow error, the electronic control unit indicates the error in dependence of the comparison. In one example, the error is indicated using a visual indicator. In another example, the error is indicated using an audio indicator.

[0022] It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the invention. Many modifications in the embodiments with regard to initializing the monitoring process and location of the temperature sensor to monitor real time temperature values are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.