CLIAMS:1 A method of controlling exhaust gas flow rate in an exhaust gas recirculation (EGR) system, the method comprising:
recording exhaust gas flow rate for a plurality of engine operating conditions;
retrieving desired exhaust gas flow rate, that corresponds to a real time engine operating condition, from said exhaust gas flow rate recorded;
determining real time exhaust gas flow rate based on differential pressure across an EGR valve and first position of said EGR valve;
calculating difference between said real time exhaust gas flow rate and said desired exhaust gas flow rate retrieved;
determining second position, of said EGR valve, that corresponds to calculated difference; and
altering said first position, of said EGR valve, to said second position, wherein alteration is used to alter said real time exhaust gas flow rate to match desired exhaust gas flow rate for said real time engine operating condition.

2 The method as claimed in claim 1, wherein method of recording exhaust gas flow rate for a plurality of engine operating conditions comprising:
determining mass of total air, flowing in an intake manifold of an engine, for said plurality of engine operating conditions;
determining mass of fresh air, flowing in said intake manifold, for said plurality of engine operating conditions;
calculating a difference value between said mass of total air and said mass of fresh air for each said plurality of engine operating conditions, said difference value representing exhaust gas flow rate that corresponds to each said plurality of engine operating conditions.

3 The method as claimed in claim 2, wherein said mass of total air, for each said plurality of engine operating conditions, is determined using a look-up table.

4 The method as claimed in claim 2, wherein said mass of fresh air, for each said plurality of engine operating conditions, is determined using a mass air flow (MAF) sensor.

5 The method as claimed in claim 1, wherein exhaust gas flow rate recorded for a plurality of engine operating conditions is stored in a look-up table.

6 The method as claimed in claim 1, wherein said differential pressure across said EGR valve is determined using at least two pressure sensors a first pressure sensor located upstream and a second pressure sensor located downstream of said EGR valve.

7 The method as claimed in claim 1, wherein said first position of said EGR valve is determined using a position sensor.

8 The method as claimed in claim 1, wherein said second position, of said EGR valve, is determined using a look-up table.
,TagSPECI:Field of the invention
[001] This invention relates to a method of controlling exhaust gas flow rate in an exhaust gas recirculation (EGR) system

Background of the invention
[002] Exhaust gas recirculation (EGR) in which exhaust gases are recirculated back into an intake manifold of an engine is a known method for reducing Nox emission for meeting emission norms. An EGR system comprises an EGR valve that controls the amount of exhaust gases that are recirculated back into the intake manifold. Desired amount of exhaust gases required for recirculation depends on position of the EGR valve and a plurality of engine operating conditions.

[003] The position of the EGR valve indicates an extent to which the EGR valve is open, thereby determining amount of exhaust gases entering into the intake manifold. The position of the EGR valve is varied to control supply of the exhaust gases, in an EGR path, based on the engine operating conditions.

[004] Sometimes position of the EGR valve is such that the desired amount of exhaust gases may not be supplied at the intake manifold. In such cases it is required that the EGR system identify real time flow of exhaust gases, in the EGR path, and further determine if such flow of exhaust gases is equal to the desired amount of exhaust gases.

[005] Conventional methods include use of a mass air flow sensor (MAF) to determine real time flow of exhaust gases in the EGR path. A feedback mechanism may be implemented to determine if the real time flow is equal to the desired amount of exhaust gases, and further the position of the EGR valve may be varied to regulate the flow of exhaust gases in case of variations between the real time flow and desired amount of exhaust gases. However, MAF sensors are expensive and hence use of MAF sensors in an EGR system may not be economical. An US patent number 6,401,700 discloses one such method of controlling the flow of exhaust gases in an EGR system.

Brief description of the accompanying drawings

[006] Figure 1 illustrates a block diagram representing a method of controlling exhaust gas flow rate in an exhaust gas recirculation (EGR) system; and

[007] Figure 2 illustrates a block diagram representing a method of recording exhaust gas flow rate for a plurality of engine operating conditions.

Detailed description

[008] Figure 1 illustrates a block diagram representing a method of controlling exhaust gas flow rate, in real time, in an exhaust gas recirculation (EGR) system. In accordance with this disclosure, the method includes the following steps: recording exhaust gas flow rate for a plurality of engine operating conditions represented as step 105, retrieving desired exhaust gas flow rate, that corresponds to a real time engine operating condition, from the exhaust gas flow rate recorded represented as step 110, determining real time exhaust gas flow rate based on differential pressure across an EGR valve and a first position of the EGR valve represented as step 115, calculating difference between the real time exhaust gas flow rate and desired exhaust gas flow rate retrieved represented as step 120, determining a second position, of the EGR valve, that corresponds to calculated difference represented as step 125 and altering the first position, of the EGR valve, to the second position represented as step 130. The alteration is used to alter the real time exhaust gas flow rate to match the desired exhaust gas flow rate for the real time engine operating condition.

[009] An electronic control unit is adapted to perform a method of controlling exhaust gas flow rate, in real time, in the EGR system. The exhaust gas flow rate refers to amount of exhaust gases flowing in an EGR path of the EGR system. The electronic control unit is configured to record exhaust gas flow rate for a plurality of engine operating conditions. The engine operating conditions may include speed, load and position of an EGR valve. The electronic control unit may store the exhaust gas flow rate recorded for different engine operating conditions in a look-up table. The exhaust gas flow rate recorded for each set of engine operating conditions represent desired exhaust gas flow rate for corresponding set of engine operating conditions. Hence, the look-up table includes desired exhaust gas flow rates for various sets of engine operating conditions. Such method of recording the exhaust gas flow rate for each set of engine operating conditions is explained in detail in conjunction with Figure 2.

[0010] Upon recording the exhaust gas flow rate for a plurality of engine operating conditions, the electronic control unit is configured to retrieve desired exhaust gas flow rate that corresponds to a real time engine operating condition. The real time engine operating condition is a sub set of the plurality of engine operating conditions. The desired exhaust gas flow rate that corresponds to the real time engine operating condition is retrieved from the look-up table that includes exhaust gas flow rate recorded for the plurality engine operating conditions. The desired exhaust gas flow rate is retrieved for determining if a real time exhaust gas flow rate is similar to the desired exhaust gas flow rate.

[0011] The electronic control unit is also configured to determine real time exhaust gas flow rate based on differential pressure across an EGR valve and a first position of said EGR valve. The real time exhaust gas flow rate refers to amount of exhaust gases flowing in an EGR path with respect to the real time engine operating condition. The differential pressure across an EGR valve is determined using at least two pressure sensors the first pressure sensor located upstream and the second pressure sensor located downstream of the EGR valve. The first position of the EGR valve indicates an extent to which the EGR valve is open, at the real time engine operating condition, and is determined using a position sensor. In some embodiments, the first position of the EGR valve is determined by measuring pressure across upstream and downstream of the EGR valve.

[0012] Using pressure sensors during determination of real time exhaust gas flow rate eliminates need for using mass air flow (MAF) sensors that are expensive.

[0013] Further, the electronic control unit is configured to calculate difference between the real time exhaust gas flow rate and the desired exhaust gas flow rate retrieved. Any difference arising between the real time exhaust gas flow rate and the desired exhaust gas flow rate indicates that the flow of exhaust gases in the EGR path is inappropriate for meeting emission norms. Further, if there is no difference between the real time exhaust gas flow rate and the desired exhaust gas flow rate then it indicates that appropriate amount of exhaust gases are recirculated in the EGR path.

[0014] Upon calculation of the difference, the electronic control unit is further configured to determine second position, of the EGR valve, that corresponds to calculated difference. The second position indicates the extent to which the EGR valve is required to be opened such that the real time exhaust gas flow rate, at the real time engine operating condition, is equal to desired exhaust gas flow rate at that engine operating condition.

[0015] Furthermore the electronic control unit is adapted to alter the first position, of the EGR valve, to the second position. Alteration may be performed using a pulse width modulation (PWM) signal having a duty cycle that corresponds to the second position and is transmitted, to the EGR valve, by the electronic control unit. Alteration of the EGR valve position from the first position to the second position enables alteration of the real time exhaust gas flow rate, at a given real time engine operating condition, to match the desired exhaust gas flow rate at that engine operating condition.

[0016] If the difference calculated is equal to zero then it indicates that the real time exhaust gas flow rate is equal to the desired exhaust gas flow rate and hence alteration of the EGR valve position is not required.

[0017] Figure 2 illustrates a block diagram representing a method of recording exhaust gas flow rate for a plurality of engine operating conditions. In accordance with this disclosure, the method includes the following steps: determining mass of total air, flowing in an intake manifold of an engine, for the plurality of engine operating conditions represented as step 205, determining mass of fresh air, flowing in the intake manifold, for the plurality of engine operating conditions represented as step 210, and calculating a difference value between the mass of total air and the mass of fresh air for each the plurality of engine operating conditions represented as step 215. Corresponding difference value represents exhaust gas flow rate for each of the plurality of engine operating conditions.

[0018] The mass of total air for a given engine operating condition refers to total capacity of air, including fresh air and exhaust gases, in the intake manifold of the engine for that engine operating condition. Hence the mass of total air varies with respect to the engine operating conditions. The mass of total air for each of the plurality of engine operating conditions is stored in a look-up table. Therefore, the mass of total air for each of the plurality of engine operating conditions is determined using the look-up table.

[0019] The mass of fresh air, for each of the plurality of engine operating conditions, is determined using a MAF sensor located at the intake manifold of the engine. The mass of fresh air that is determined for each of the plurality of engine operating conditions is further stored in a look-up table. The MAF sensor is merely used to determine the mass of fresh air for storing the mass values in the look-up table. However, the MAF sensor is not used to determine real time flow of exhaust gases in subsequent stages and hence can be removed from the EGR system once the look-up table is prepared.

[0020] Further a difference value between the mass of total air and the mass of fresh air for each of the plurality of engine operating conditions is calculated. The difference value represents exhaust gas flow rate that corresponds to each of the plurality of engine operating conditions. Also, the exhaust gas flow rate calculated for each the plurality of engine operating conditions is stored in a look-up table. The exhaust gas flow rate calculated for a given engine operating condition represents the desired exhaust gas flow rate, required for recirculation, for that engine operating condition. Therefore, the desired exhaust gas flow rate for any engine operating condition can be retrieved from this look-up table.

[0021] In the present disclosure, recording exhaust gas flow rate values for various sets of engine operating conditions and further storing recorded values in a look-up table eliminates the need for using MAF sensors in the EGR system. Also, use of pressure sensors for determining the exhaust gas flow rate in real time eliminates need for calculating fresh air mass for determining such exhaust gas flow rate. Thereby, MAF sensor that is expensive can be replaced by low cost pressure sensors.

[0022] One working example for the first position and the second position of the EGR valve is hereinafter explained. In the working example the first position, of the EGR valve, may correspond to the EGR valve being open by 20% for a particular real time engine operating condition. The EGR valve being open by 20% corresponds to a specific exhaust gas flow rate in the EGR system. However, the exhaust gas flow rate that corresponds to the first position may not be equal to the desired exhaust gas flow rate for that engine operating condition and hence the EGR valve position may be required to be varied to a second position. The second position may correspond to the EGR valve being opened by 50% so that the exhaust gas flow rate that corresponds to 50% of the valve opening may be equal to the desired exhaust gas flow rate. In another working example, the first position, of the EGR valve, may correspond to the EGR valve being open by 60%. However, the exhaust gas flow rate that corresponds to the first position, where the EGR valve is being open by 60%, may not be equal to the desired exhaust gas flow and hence the EGR valve position may be required to be varied to a second position. The second position may correspond to the EGR valve being opened by 25%.

[0023] It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to recording the exhaust gas flow rate, location of the pressure sensors to determine real time exhaust gas flow rate are envisaged and form a part of this invention. Also, the disclosure does not limit the EGR valve positions to merely first position and second position. There may be various other positions of the EGR valve. The scope of the invention is only limited by the claims.