CLIAMS:I claim:
1. A method for an exhaust gas recirculation (EGR) control for an engine, said method comprising:
determining an estimated fuel quantity for an engine speed, comprising:
receiving an engine speed of a vehicle in time domain from an engine speed sensor;
transforming the engine speed in time domain to a frequency domain data;
compensating for a plurality of engine parameters based on the transformed frequency domain data;
calculating the estimated fuel quantity for the engine speed based on the compensated engine parameters;
calculating a corrected fuel quantity based on the estimated fuel quantity and an indicated fuel quantity; and
calculating the EGR duty cycle for the engine based on the corrected fuel quantity and the engine speed.

2. The method as claimed in claim 1, wherein the indicated fuel quantity is based on a position of an accelerator pedal.

3. The method as claimed in claim 1, wherein the indicated fuel quantity is based on a position of the engine speed.

4. An electronic control unit (ECU) for an exhaust gas recirculation (EGR) control for an engine, said ECU adapted to
determine an estimated fuel quantity for an engine speed, comprising:
receiving an engine speed of a vehicle in time domain from an engine speed sensor;
transforming the engine speed in time domain to a frequency domain data;
compensating for a plurality of engine parameters based on the transformed frequency domain data;
calculating the estimated fuel quantity for the engine speed based on the compensated engine parameters;
calculate a corrected fuel quantity based on the estimated fuel quantity and an indicated fuel quantity; and
calculate the EGR duty cycle for the engine based on the corrected fuel quantity and the engine speed. ,TagSPECI:The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention
[001] The invention relates to an exhaust gas recirculation (EGR) control for an engine.

Background of the invention
[002] During the operation of an internal combustion engine, undesirable pollutant gases are generated. An exhaust gas recirculation (EGR) system is used to control the generation such undesirable pollutant gases. The EGR system recirculates exhaust gas by-products generated during the combustion process into the intake air supply of the internal combustion engine. The exhaust gas by-products introduced into the engine cylinders reduces the available oxygen, thereby reducing the formation of nitrous oxides (NOx).

[003] An engine torque is estimated based on the oscillations in the engine speed. The estimated engine torque is used to correct a desired air mass based on the estimated injection quantity by evaluating the engine speed. This correction in turn is used to adjust the EGR flow. Currently, an air mass flow sensor is required for correcting the desired air mass using the estimated engine torque to adjust the EGR flow. There is a need for a method to correct and control the EGR flow using the estimated engine torque in the absence of the air mass flow sensor.

[004] The patent application, WO2013018895, discloses an air flow rate sensor calibration device which enables control for completely shutting off EGR during traveling without increasing NOx emission and enables improvement in the detection accuracy of intake air quantity. An air flow rate sensor calibration device is provided with: an engine brake detection unit which detects that the speed is being reduced by the activation of an engine brake caused by the release of an accelerator during traveling; an EGR complete shut-off control unit which performs control for completely shutting off an EGR valve while the speed is being reduced by the activation of the engine brake; a basic formula calculation unit which calculates the intake air quantity by a basic formula when EGR is completely shut-off; a volumetric efficiency correction calculation unit which corrects and calculates a variation in volumetric efficiency by multiplying the value calculated by the basic formula by a correction term; a calibrated value storage unit which learns a difference between the calculated value of the intake air quantity and the detected value of the intake air quantity by an MAF sensor and stores the difference as the calibrated value; and a calibration calculation unit which adds the calibrated value to the detected value of the intake air quantity by the MAF sensor and sets the result as the intake air quantity.

Short description of the drawing
[005] An exemplifying embodiment of the invention is explained in principle below with reference to the drawing. The drawing is,
[006] Figure 1 illustrates the method of using an electronic control unit (ECU) for an exhaust gas recirculation (EGR) control for an engine in accordance with this invention.

Description of the invention
[007] Figure 1 illustrates the method of using an electronic control unit (ECU) for an exhaust gas recirculation (EGR) control for an engine. In step S1, the ECU is adapted to determine the estimated fuel quantity for the engine speed. The ECU receives an engine speed of a vehicle in time domain from an engine speed sensor; transforms the engine speed in time domain to a frequency domain data; compensates for a plurality of engine parameters based on the transformed frequency domain data; and calculates the estimated fuel quantity for the engine speed based on the compensated engine parameters. In step S2, the ECU is adapted to calculate the corrected fuel quantity based on the estimated fuel quantity and the indicated fuel quantity. In step S3, the ECU is adapted to calculate the EGR duty cycle for the engine based on the corrected fuel quantity and the engine speed.

[008] Factors such as reduction in fuel filter efficiency, use of low quality fuel in the engine, etc., cause drift in the injection of fuel to a fuel injection system of the engine. The drift in injection of fuel causes a shift in an operating point of injectors of the fuel injection system. An engine speed sensor senses the engine speed of a vehicle. The ECU receives the engine speed of the vehicle in time domain from the engine speed sensor. The ECU transforms the engine speed in time domain to a frequency domain data. When the ECU transforms the engine speed in time domain to the frequency domain data, the ECU reveals the frequencies embedded in the engine speed. The frequencies embedded are, for example, crank frequency, cam frequency, ignition frequency, etc. The ECU thus enables easy evaluation of the frequencies in the frequency domain.

[009] The drift in the injection of fuel to the fuel injection system causes change in the operating point of engine parameters, for example, fuel quantity, boost pressure, oscillating masses, etc. Drift in fuel supplied to the fuel injection system also causes change in the air system of the engine. This drift in fuel supplied to the fuel injection causes change in the amplitude of the embedded frequencies, for example, injection frequency, of the engine speed. The ECU compensates for the engine parameters such as boost pressure and oscillating masses based on the change in the amplitude of the embedded frequencies.

[0010] The ECU calculates the estimated fuel quantity required for the engine speed. The ECU refers to a database for a value the estimated fuel quantity corresponding to the compensated engine speed in frequency domain. The database comprises a list of prestored values of compensated engine speed and the corresponding value of estimated fuel quantity for each of the compensated engine speed.

[0011] In an embodiment, the indicated fuel quantity is based on a position of an accelerator pedal. The pressure exerted on the accelerator pedal by the user provides a torque which is converted to an equivalent fuel quantity. This equivalent fuel quantity is the indicated fuel quantity. The ECU refers to the database for a value the indicated fuel quantity corresponding to the torque due to the pressure exerted on the accelerator pedal by the user. The database comprises a list of prestored values of the torque due to the pressure exerted on the accelerator pedal and the corresponding value of indicated fuel quantity for each value of the torque due to the pressure exerted on the accelerator pedal.

[0012] In another embodiment, the indicated fuel quantity is based on a position of the engine speed. The ECU refers to the database for a value the indicated fuel quantity corresponding to a value of the engine speed. The database comprises a list of prestored values of the torque due to the pressure exerted on the accelerator pedal and the corresponding value of indicated fuel quantity for each value of the torque due to the pressure exerted on the accelerator pedal.

[0013] The ECU calculates the difference between the estimated fuel quantity to maintain the engine speed and the indicated fuel quantity. The difference is the corrected fuel quantity to maintain the engine speed.

[0014] The ECU calculates the EGR duty cycle for the engine based on the corrected fuel quantity and the engine speed. The ECU refers to the database to obtain the value of the EGR duty cycle for the engine corresponding to the values of the corrected fuel quantity and the engine speed. The database comprises a list of values of the corrected fuel quantity and the engine speed and a corresponding value of the EGR duty cycle for each combination of the values of the corrected fuel quantity and the engine speed.

[0015] The ECU thus controls the EGR duty cycle for the engine. The ECU can be used in applications where the air flow mass sensors are absent for EGR control to achieve better emission consistency. When there is no air mass flow sensor, then the EGR for the engine can be controlled based on the engine speed and the corrected fuel quantity.

[0016] It must be understood that the embodiments explained in the above detailed description is only illustrative and does not limit the scope of this invention. The scope of this invention is limited only by the scope of the claims. Many modification and changes in the embodiments aforementioned are envisaged and are within the scope of this invention.