KR20230083772A - EGR flow control system and method for reducing knock generation of engine - Google Patents

Abstract

The present invention relates to an EGR flow control system and control method for a vehicle and, more specifically, to an EGR flow control system and method for reducing engine knock, which can improve the fuel efficiency of the vehicle by minimizing engine torque loss according to the recognition of an ignition timing when an engine knock is generated. The EGR flow control method of a vehicle according to the present invention comprises: a step of activating an EGR system when the EGR system operation condition is satisfied after the warming up of an engine; a step of performing the recognition of the ignition timing for knock reduction when it is checked that the knock is generated by determining a knock occurrence of the engine after the EGR system is activated; a step of determining whether the recognition of the ignition timing by the knock occurrence of the engine occurs at a first setting value or more; a step of increasing an EGR usage rate to a second setting value or more through EGR flow rate control when it is checked that the recognition of the ignition timing occurs at the first setting value or more, and advancing the ignition timing to maintain an ignition timing value before the recognition of the ignition timing occurs; and a step of determining whether to store a current EGR usage rate increase value by determining whether engine roughness deteriorates by a certain level or more when it is checked that the engine knock is no longer generated.

Description

EGR flow control system and method for reducing knock generation of engine

The present invention relates to an EGR flow rate control system and control method of a vehicle, and more particularly, to an engine knock that can improve fuel efficiency of a vehicle by minimizing engine torque loss due to ignition timing delay when engine knock occurs. It relates to an EGR flow rate control system and method for generation reduction.

Exhaust gas from a vehicle engine contains a large amount of harmful components such as CO, HC, and NOx (nitrogen compounds). In particular, since the amount of NOx generated increases as the combustion temperature of the engine increases, it is necessary to reduce the combustion temperature of the engine in order to reduce the amount of NOx included in the exhaust gas.

As a method of lowering the combustion temperature of an engine in order to reduce the amount of NOx, a part of the exhaust gas is included in the intake mixture and introduced into the combustion chamber to lower the combustion temperature of the engine by lowering the density of the mixture without changing the air-fuel ratio of the mixture itself. An EGR system is being applied.

The EGR (Exhaust Gas Recirculation) system can reduce the amount of NOx by lowering the temperature of the combustion chamber, and at the same time, it can reduce engine knock and advance the ignition timing. Accordingly, the output and fuel efficiency of the engine can be improved.

However, in the conventional EGR system, when an engine knock occurs, avoidance control is performed through ignition timing retard, resulting in a loss of engine torque (output), thereby reducing fuel efficiency of the vehicle.

In addition, in the conventional EGR system, when controlling the EGR flow rate flowing into the combustion chamber through the EGR valve, it is a method that is fixedly controlled with a value set (targeting) for each driving area of the vehicle, so it changes according to the driving conditions of the vehicle. There was a problem that it was difficult to properly respond to the combustion characteristics to be.

Korean Patent Publication No. 2016-0070268 (2016.06.20)

The present invention has been made to solve the above problems, and the technical problem to be solved in the present invention is to control the EGR flow rate and ignition timing flowing into the engine when knocking of the engine occurs during vehicle operation to An object of the present invention is to provide an EGR flow rate control system and method for reducing engine knock that can minimize engine torque loss due to delayed ignition timing.

An EGR flow rate control system for reducing knock of an engine according to the present invention for solving the above technical problems includes a knock sensor for detecting a knock generated in an engine; a speed sensor for detecting the rotational speed and rotational angle of the crankshaft; and a controller that determines whether or not engine knock has occurred based on signals input from the knock sensor and the speed sensor and controls the EGR flow rate flowing into the engine and the engine ignition timing. When it is determined that the delay is greater than the first set value, the EGR usage rate is increased to the second set value or higher through the EGR flow control, and the ignition timing is advanced to maintain the ignition timing value at the time before the ignition timing delay occurs. characterized by

Here, the first set value may be a value of 3° based on a crank angle.

In addition, the second set value may be 1.5% based on the EGR usage rate.

Further, the control unit may control the process of increasing the EGR usage rate to the second set value or higher and advancing the ignition timing to be repeatedly performed until knocking of the engine does not occur.

In addition, when it is confirmed that knock of the engine no longer occurs through the process of increasing the EGR usage rate to the second set value or higher and advancing the ignition timing, the controller deteriorates the engine roughness beyond a certain level. It is determined whether or not the current EGR usage rate increase value is stored or not.

In this case, if it is determined that the engine roughness is not deteriorated beyond a certain level, the control unit may store the current EGR usage rate increase value in the corresponding driving area as a learning value.

In addition, the control unit may reset the current EGR usage rate increase value when it is determined that the engine roughness has deteriorated beyond a certain level.

Meanwhile, an EGR flow rate control method for reducing engine knock according to the present invention includes: (a) activating the EGR system when an EGR system operating condition is satisfied after engine warm-up; (b) determining whether engine knock occurs after the EGR system is activated, and if it is confirmed that knock has occurred, performing ignition timing retardation for knock reduction; (c) determining whether ignition timing delay due to knocking of the engine is greater than or equal to a first set value; (d) When it is confirmed that the ignition timing delay is greater than the first set value, the EGR usage rate is increased to the second set value or higher through the EGR flow control, and the ignition timing value at the point before the ignition timing delay occurs is maintained. advancing the ignition timing; (e) if it is confirmed that knocking of the engine no longer occurs, determining whether engine roughness has deteriorated to a predetermined level or more, and determining whether to store the current EGR usage rate increase value; It is characterized in that it includes.

Here, the step (a) includes: (a-1) determining whether the current operating condition of the vehicle satisfies an EGR system operable condition after engine warm-up; (a-2) determining whether engine RPM and load fluctuations are less than or equal to a reference value in a section where engine knock control is activated while the vehicle is running, when the driving condition of the vehicle satisfies the EGR system operable condition; and ; (a-3) activating the EGR system to selectively increase the EGR usage rate in a specific operating region when the engine RPM and load fluctuations are less than or equal to the reference value;

In step (a-1), the EGR system satisfies the operable conditions when the coolant temperature is 70°C or higher, the air filling rate is 35% or higher, and the vehicle speed is 30Km/h or higher. can judge

In addition, in the step (a-1), it may be determined that the EGR system satisfies the operable condition when failures of the knock sensor, the speed sensor, and the oxygen sensor are not detected.

In the step (a-2), the reference value for RPM may be an engine rotation acceleration of 20 revolution/s ² per cycle.

In addition, in the step (a-2), the reference value for the load variation of the engine may be an intake pressure of 200 hPa per time of 50 ms.

In addition, the first set value in step (c) may be a value of 3° based on a crank angle.

In addition, the second set value of step (d) may be 1.5% based on the EGR usage rate.

And, if it is determined that the engine roughness has not deteriorated beyond a certain level in step (e), the EGR usage rate may be learned by storing the current EGR usage rate increase value as a learning value in the corresponding driving area.

In addition, if it is determined that the engine roughness has deteriorated beyond a certain level in the step (e), the current EGR usage rate increase value may be reset.

According to the EGR flow control system and control method of the present invention, it is possible to increase the fuel efficiency of the engine by minimizing engine torque loss due to delayed ignition timing through controlling the EGR flow rate and ignition timing when engine knock occurs during vehicle operation. It has the advantage of improving the fuel efficiency of the vehicle.

In addition, when engine knock occurs, it is possible to reduce the occurrence of engine knock by limitingly increasing the EGR flow rate together with the advance of the ignition timing, and deteriorating drivability by additionally checking the engine roughness condition that may be caused by the increased EGR flow rate. It has the advantage that more robust engine control is possible because it determines whether or not the

In addition, a learning function is added to store and use the optimal EGR usage rate increase value that does not deteriorate engine roughness while reducing engine knock in the driving area where the EGR flow rate is increased as a new learning value, which is advantageous in terms of fuel efficiency. It has the advantage of being able to use continuously.

1 is a configuration diagram showing the flow of input and output signals between an input unit, a control unit, and an output unit in an EGR flow rate control system for reducing engine knock according to the present invention;
Figure 2 is a block diagram showing the overall configuration of the EGR flow rate control system according to the present invention.
3 is a flowchart sequentially showing an EGR flow rate control method according to the present invention.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention.

However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. In addition, parts marked with the same reference numerals throughout the detailed description indicate the same components.

Hereinafter, embodiments of an EGR flow rate control system and control method for reducing engine knock according to the present invention will be described in detail with reference to the accompanying drawings.

1 shows the flow of input and output signals between an input unit, a control unit, and an output unit in the EGR flow control system for reducing engine knock according to the present invention, and FIG. 2 is the overall configuration of the EGR flow control system according to the present invention. This is a block diagram showing

Referring to FIGS. 1 and 2 , the EGR flow rate control system of a vehicle for reducing knock occurrence of an engine according to the present invention is a system that can be applied to a gasoline engine to which an EGR (Exhaust Gas Recirculation) system is applied, and a knock sensor 110 ) and a speed sensor 120, an input unit 100, a control unit (ECU) 200, and an output unit 300 including an EGR valve 310 and an ignition coil 320. .

The knock sensor 110 constituting the input unit 100 may be installed on an outer wall between cylinders of an engine to detect knock generated from an engine cylinder.

In addition, the speed sensor 120 is a sensor mounted on the engine and capable of detecting the rotational speed, rotational angle, rotational acceleration, etc. of a crankshaft, and a crankshaft position sensor may be used.

The control unit 200 determines whether or not engine knock has occurred based on signals input from the knock sensor 110 and the speed sensor 120 and adjusts the opening amount of the EGR valve 310 to adjust the EGR flow rate flowing into the engine ( The flow rate of exhaust gas recirculated to the engine) can be flexibly controlled, and the ignition timing of the engine can be controlled by applying a control signal to the ignition coil 320 .

The EGR valve 310 constituting the output unit 300 can adjust the flow rate of exhaust gas flowing into the engine side, that is, the EGR flow rate, in the EGR system for recirculating a part of the exhaust gas burned in the engine to the engine.

In addition, the ignition coil 320 is activated according to a voltage or a pulse-type control signal input from the control unit 200 and generates an ignition spark through a spark plug by inducing a high voltage. Accordingly, the control unit 200 may control the ignition timing of the engine by determining the ignition timing according to whether engine knock occurs, engine load and rotational speed, throttle valve opening, coolant temperature, intake air temperature, and the like.

Specifically, the control unit 200 may analyze whether engine knock has occurred, engine roughness based on engine rotational acceleration, etc. based on signals input from the knock sensor 110 and the speed sensor 120. It is possible to control the amount of EGR flowing into the engine and the ignition timing of the engine through the control of the EGR valve 310 and the ignition coil 320 by determining whether knocking of the engine has occurred.

In general, the knock phenomenon that occurs in an engine changes depending on the shape of the combustion chamber, the deposits in the combustion chamber, the composition of the mixture, the shape of the intake manifold, the quality of the fuel, the air density, the temperature of the engine, etc. Since knock has a close relationship with the ignition timing of the engine above all else, control to retard the ignition timing is performed in order to reduce the occurrence of knock in normal control. In this case, if the ignition timing is delayed too much, there is a problem in that torque (output) loss of the engine is caused because the explosion pressure in the combustion chamber of the engine is lowered and the output of the engine is also lowered correspondingly.

In this way, in order to prevent engine torque from being reduced by retarding the ignition timing according to the control logic set for knock reduction when engine knock occurs, in the present invention, the control unit 200 retardes the ignition timing due to engine knock. When it is determined that the first set value or more has occurred, the EGR flow rate flowing into the engine through the EGR valve 310 is increased to increase the EGR usage rate (%) above the second set value, and ignition By advancing the timing and controlling it to maintain the ignition timing value immediately before the ignition timing retarded, it is possible to reduce engine knock and minimize engine torque loss caused by retarding the ignition timing to avoid knock. there is.

In this case, the first set value, which is set as a reference value for determining whether ignition timing is excessively delayed due to engine knock, may be applied as a crank angle reference value of 3°. That is, when it is confirmed that the ignition timing delay has occurred at a crank angle of 3° or more due to engine knock, the control unit 200 increases the EGR flow rate to the second set value or higher and sets the ignition timing to the ignition timing immediately before the delay. It is possible to perform control of advancing to a timing value.

In addition, when controlling the increase in the EGR usage rate (%), a value of 1.5% based on the EGR usage rate (%) may be applied as the second set value set as the reference value. Therefore, when the ignition timing is delayed by more than 3 degrees in the crank angle, the control unit 200 increases the EGR flow rate by adjusting the opening of the EGR valve 310 and controls the EGR utilization rate (%) to be maintained at least 1.5%. can do.

At this time, in the control unit 200, the control process of increasing the EGR usage rate to 1.5% or more and advancing the ignition timing to the ignition timing value immediately before the ignition timing is delayed until it is confirmed that no engine knock has occurred. It can be controlled to perform repeatedly.

In addition, the control unit 200 repeatedly performs the control process of increasing the EGR usage rate by 1.5% or more and advancing the ignition timing as described above, and when it is confirmed that engine knock no longer occurs, the EGR flow rate in the engine combustion chamber is increased. It is additionally determined whether engine roughness has deteriorated beyond a certain level due to combustion instability caused by combustion, and the optimal EGR usage rate increase value that reduces knock and does not deteriorate engine roughness is set as a new learning value. You can decide whether or not to save.

Specifically, the control unit 200 diagnoses the current state of engine roughness after the occurrence of knock is reduced, and when it is confirmed that the engine roughness has not deteriorated beyond a certain level (set reference value), in the corresponding driving area. The currently used EGR usage rate increase value may be stored as a learning value. In this case, the EGR usage rate increase value stored as the learning value may be continuously applied to control the EGR usage rate and ignition timing upon entering the corresponding operation region until a decision to reset the EGR usage rate is made.

Conversely, when knocking is reduced through the increase in the EGR flow rate by the control process, but it is determined that the engine roughness has deteriorated to a certain level or more due to the increase in the EGR flow rate in the engine combustion chamber, side effects due to the increase in the EGR flow rate have occurred. Since it can be seen as a case, it is possible to reset the EGR usage rate increment value used in the control process of the corresponding operation area so as not to use it again in the corresponding operation area in the future.

On the other hand, Figure 3 (Fig. 3a, 3b) is a flow chart showing the EGR flow rate control method using the above-described EGR flow rate control system of the present invention sequentially.

Referring to FIG. 3 , an EGR flow rate control method for reducing engine knock according to the present invention includes activating the EGR system when an EGR system operating condition is satisfied after engine warm-up; determining whether an engine knock occurs after the EGR system is activated, and if it is confirmed that knock has occurred, performing ignition timing retardation for knock reduction; determining whether an ignition timing delay due to engine knock occurs at a first set value or more; When it is confirmed that the ignition timing retardation has occurred above the first set value, the EGR usage rate is increased to the second set value or higher through the EGR flow control, and the ignition timing is set to maintain the ignition timing value prior to the ignition timing retardation. advancing step; and determining whether or not to store the current EGR usage rate increase value by determining whether engine roughness has deteriorated to a predetermined level or more, when it is determined that knocking of the engine no longer occurs. there is.

Specifically, in the first step, after warming up the engine, it is determined whether or not the current driving condition of the vehicle satisfies the EGR system operable condition (S410).

In this case, as the operating conditions of the EGR system, it may be determined that the EGR system operating conditions are satisfied when the cooling water temperature is 70° C. or higher, the air filling rate is 35% or higher, and the vehicle speed is 30 km/h or higher. In addition, when failures of the knock sensor, speed sensor, and oxygen sensor are not detected, it may be determined that the EGR system satisfies the operable condition.

If it is determined that the driving condition of the vehicle satisfies the condition for enabling the EGR system to operate from the step (S410), whether or not the RPM and load variation of the engine are below the reference value in the section where the knock control of the engine is activated while the vehicle is driving. Determine. (S420)

In this case, the reference value for the RPM may be an engine rotational acceleration value of 20 revolution/s ² per cycle, and the reference value for the load variation of the engine may be applied as an intake pressure value of 200 hPa per time 50 ms.

If it is confirmed from the above step (S420) that the RPM and load fluctuation of the engine are less than the reference value, the EGR system is activated to selectively increase the EGR usage rate within a specific operating area (S430).

And, after the EGR system is activated, signals input from the knock sensor 110 and the speed sensor 120 are analyzed to determine whether engine knock has occurred. In this case, if it is confirmed that knock has occurred, ignition timing for knock reduction is performed according to the set control logic.

Next, the control unit 200 determines whether or not ignition timing due to knocking of the engine has occurred above a first set value (S440).

In this case, as a first set value that is a criterion for determining whether ignition timing is excessively delayed, a crank angle reference value of 3° may be applied.

When it is confirmed that the delay in the ignition timing is greater than the first set value in the step (S440), the control unit 200 outputs a control signal to the EGR valve 310 and the ignition coil 320 to control the EGR flow rate. Through this, the EGR usage rate (%) is increased to the second set value or more, and the ignition timing is advanced to maintain the ignition timing value at the point before ignition timing retardation occurs (S450).

At this time, as the second set value serving as the standard when controlling the increase in the EGR utilization rate (%), a value of 1.5% based on the EGR utilization rate (%) may be applied.

That is, when the controller 200 determines that the ignition timing is delayed due to knocking of the engine during vehicle operation and that the perceived level of the ignition timing exceeds 3° based on the crank angle, the EGR valve 310 It is possible to increase the EGR flow rate through the control so that the EGR usage rate can be increased by 1.5% or more under the corresponding operating conditions.

Next, the control unit 200 checks whether or not knock has been reduced by the control process of step S450. When it is confirmed that there is no change in the generation trend, the EGR amount is repeatedly increased by 1.5% or more until the point at which knocking no longer occurs.

Here, when there is no change in the knock occurrence tendency even though the EGR usage rate is increased to the set maximum value (eg, 6%) through the repeated EGR flow rate increase control as described above, the increased EGR usage rate can be reset to an initial state.

Next, when it is confirmed from the above step (S460) that knocking of the engine no longer occurs, it is determined whether or not the engine roughness has deteriorated beyond a certain level (S470).

Here, the engine roughness is an index used to determine misfiring, and the 'certain level' value mentioned in the step (S470) is applied at a level of 70% compared to the standard roughness value used as a criterion for misfiring determination. can At this time, the misfiring determination criterion roughness value may be set differently for each operation region (set according to RPM and Torque).

Here, in spite of increasing the EGR usage rate through the EGR flow rate control, if the knock reduction effect is insignificant and the EGR usage ratio is continuously increased, combustion instability may occur inside the combustion chamber due to excessive EGR usage, resulting in deterioration of engine roughness. can

In particular, when engine roughness deteriorates beyond a certain level due to excessive use of the EGR flow rate, combustion instability may occur, which may increase exhaust gas or cause discomfort due to engine vibration to vehicle occupants.

Therefore, in the present invention, it is possible to determine whether the EGR usage rate increase value will be used as a learning value in the future by determining whether the engine roughness deteriorates to a certain level or less even after knocking is reduced through the EGR usage rate increase control.

Here, when it is determined that the engine roughness has not deteriorated to a certain level or higher from the step (S470), the EGR utilization rate can be learned by storing the EGR utilization rate increment value currently used in the corresponding driving area as a learning value. (S490)

In other words, if engine knock is reduced according to the EGR usage rate increase control and it is confirmed that the change in engine roughness is maintained at a stable level, the condition is stored as a learning value and used as a learning value when the same driving condition is entered in the future. It can be controlled with the optimized EGR flow rate and ignition timing values stored.

On the other hand, when it is determined that the engine roughness has deteriorated to a certain level or more from the step (S470), the currently used EGR usage rate increment value is reset. (S480)

That is, when the knock reduction effect through the increase in the EGR use rate is insignificant or side effects, such as deterioration of the engine roughness due to the increase in the EGR flow rate, occur, the EGR use rate increase value may be initialized so that the EGR flow rate increase function is not applied. .

As described above, according to the EGR flow rate control system and control method of the present invention, when engine knock occurs during vehicle operation, engine torque loss due to late ignition timing is minimized through control of the EGR flow rate and ignition timing to increase fuel efficiency of the engine. And, through this, it is possible to improve the fuel efficiency of the vehicle.

In addition, when engine knock occurs, it is possible to reduce the occurrence of engine knock by limitingly increasing the EGR flow rate along with the advance of the ignition timing, and deteriorating drivability by additionally checking the engine roughness condition that may be caused by the increased EGR flow rate. Since it determines whether or not there is a problem, more robust engine control may be possible.

In addition, a learning function is added to store and use the optimum EGR usage rate increment value that does not deteriorate engine roughness while reducing engine knock in the driving area where the EGR flow rate is increased as a new learning value, which is advantageous in terms of fuel economy. can be used continuously.

Although preferred embodiments of the present invention have been described above, the scope of the present invention is not limited to such specific embodiments, and those skilled in the art can make appropriate changes within the scope described in the claims of the present invention. this will be possible

100: input unit 110: knock sensor
120: speed sensor 200: control unit
300: output unit 310: EGR valve
320: ignition coil

Claims (17)

a knock sensor that detects knock generated in the engine;
a speed sensor that detects the rotational speed and rotational angle of the crankshaft;
A control unit that determines whether engine knock occurs based on signals input from the knock sensor and the speed sensor and controls the amount of EGR flowing into the engine and the engine ignition timing;
When it is determined that the delay in ignition timing is greater than or equal to the first set value due to engine knock, the control unit increases the EGR usage rate to more than the second set value through EGR flow rate control, and the time before the delay in ignition timing occurs. An EGR flow control system for reducing knock of an engine, characterized in that the ignition timing is advanced to maintain the ignition timing value.
The EGR flow control system according to claim 1, wherein the first set value is a crank angle of 3°.
The EGR flow control system according to claim 1, wherein the second set value is 1.5%.
The engine knock of claim 1 , wherein the control unit controls the process of increasing the EGR usage rate to a second set value or higher and advancing the ignition timing to be repeatedly performed until engine knock does not occur. EGR flow control system for generation reduction.
The method of claim 1, wherein the control unit increases the EGR usage rate to a second set value or more and advances the ignition timing, and when it is confirmed that knock of the engine no longer occurs, engine roughness is determined. An EGR flow control system for reducing knock occurrence of an engine, characterized in that it determines whether or not the current EGR usage rate increase is stored by determining whether the deterioration has exceeded a certain level.
6. The engine of claim 5 , wherein the control unit stores a current EGR usage rate increase value in a corresponding driving area as a learning value when it is determined that the engine roughness has not deteriorated beyond a certain level. EGR flow control system to reduce knocking.
The method of claim 5 , wherein the control unit resets a current EGR usage rate increase value when it is determined that the engine roughness deteriorates to a predetermined level or more. EGR flow control system.
(a) activating the EGR system when an EGR system operating condition is satisfied after engine warm-up;
(b) determining whether or not engine knock occurs after the EGR system is activated, and if it is confirmed that knock has occurred, performing ignition timing retardation for knock reduction;
(c) determining whether ignition timing delay due to knocking of the engine is greater than or equal to a first set value;
(d) When it is confirmed that the ignition timing retardation has occurred at or above the first set value, the EGR usage rate is increased to the second set value or higher through the EGR flow control, and the ignition timing value at the point before the ignition timing retard occurs is maintained. advancing the ignition timing;
(e) determining whether engine roughness has deteriorated to a predetermined level or higher, and determining whether to store a current EGR usage rate increase value when it is determined that knocking of the engine no longer occurs;
EGR flow rate control method for reducing the occurrence of knock of the engine, characterized in that it comprises a.
The method of claim 8, wherein step (a),
(a-1) determining whether the current driving condition of the vehicle satisfies the EGR system operable condition after engine warm-up;
(a-2) determining whether RPM and load variation of the engine are equal to or less than a reference value in a section in which knock control of the engine is activated while the vehicle is driving, when the driving condition of the vehicle satisfies the EGR system operable condition;
(a-3) activating the EGR system to selectively increase an EGR usage rate in a specific operating region when the engine RPM and load variation are less than or equal to the reference value;
EGR flow rate control method for reducing the occurrence of knock of the engine, characterized in that it comprises a.
The method of claim 9, wherein the operating condition of the EGR system in step (a-1) is,
An EGR flow rate control method for reducing engine knock, characterized in that it is determined that the EGR system satisfies operating conditions when the coolant temperature is 70 ° C. or higher, the air filling rate is 35% or higher, and the vehicle speed is 30 km / h or higher.
The method of claim 9, wherein the operating condition of the EGR system in step (a-1) is,
An EGR flow rate control method for reducing knock occurrence of an engine, characterized in that it is determined that the EGR system satisfies an operable condition when failures of the knock sensor, the speed sensor, and the oxygen sensor are not detected.
10. The method of claim 9, wherein the reference value for the RPM in step (a-2) is an engine rotation acceleration per cycle of 20 revolution/s ² . .
10. The method of claim 9, wherein the reference value for the engine load variation in step (a-2) is an intake pressure of 200 hPa per time of 50 ms.
The method of claim 8, wherein the first set value in step (c) is a crank angle of 3°.
The method of claim 8, wherein the second set value in step (d) is 1.5%.
The method of claim 8 , wherein in the step (e), if it is determined that the engine roughness has not deteriorated beyond a certain level, the current EGR usage rate increase value in the corresponding driving area is stored as a learning value to learn the EGR usage rate. EGR flow rate control method for reducing knock occurrence of an engine, characterized in that.
9. The method of claim 8 , wherein if it is determined that the engine roughness has deteriorated to a certain level or more in the step (e), the current EGR usage rate increment value is reset. EGR flow rate control method for

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