KR20040098263A - Exhaust gas recirculation control system of diesel vehicle and method thereof - Google Patents

Abstract

PURPOSE: An EGR(Exhaust Gas Recirculation) control device of a diesel vehicle and a method thereof are provided to stabilize exhaust gas, and to reduce deviation of exhaust gas by controlling EGR feedback with a lambda sensor. CONSTITUTION: An EGR control device comprises an engine rpm detecting unit(10) measuring rpm of the engine; an engine load detecting unit(20) detecting fluctuation of load of the engine; a coolant temperature detecting unit(30) measuring temperature of coolant; a lambda sensor(40) detecting density of oxygen among exhaust gas; a control unit(50) setting the desired lambda value for EGR feedback control according to engine rpm, engine torque and compensation variables, and duty-controlling an EGR valve(60) to increase the oxygen among exhaust gas to the desired lambda value according to signals from the lambda sensor; and the EGR valve regulating recirculation of exhaust gas.

Description

EXHAUST GAS RECIRCULATION CONTROL SYSTEM OF DIESEL VEHICLE AND METHOD THEREOF

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to exhaust gas recirculation (EGR) control in diesel vehicles. More specifically, EGR feedback control is performed using a signal of a lambda sensor mounted on the exhaust side. An apparatus and method for controlling exhaust gas recirculation of a diesel vehicle which is adapted to provide stability of the exhaust gas by performing.

In general, there are various exhaust gas recirculation control methods applied to diesel engines, but they can be roughly divided into three types.

The first method is to control the position of the EGR valve, which allows the control position of the EGR valve to be determined in advance in the predetermined operating area, and the position of the EGR valve can be controlled. The sensor used is an EGR valve mounted on the upper surface of the EGR valve. It is a lift sensor, and the working fluid is controlled by using the negative pressure generated by the engine.

The disadvantage of the method of controlling the position of the EGR valve is that the actual amount of EGR flow fluctuates greatly when the defined driving range is changed between the production vehicles or when the boost pressure and the back pressure change, resulting in fluctuations in the exhaust gas. There is a possibility to derive

Secondly, the virtual position of the EGR valve is controlled, which is a method of calculating the virtual position of the EGR valve using a duty ratio controlling the EGR valve and performing self-feedback control using the same.

This method also results in a control of the EGR valve by applying a fixed duty ratio as a result, as in the first position control method, there is a disadvantage in that the variation of the EGR flow due to the deviation between the vehicles cannot be prevented.

Third, the feedback control method using the air flow sensor, which is currently applied to most common rail diesel mass production vehicles, the amount of air detected by the air flow sensor (AFS) mounted on the intake (except the EGR flow) Feedback is controlled using the actual clean air flowing from the

This is roughly described with reference to FIG. 5 as follows.

The engine control means (not shown) detects the engine speed and the fuel injection amount in the current driving state and compares it with the data set in the map table to set a target air amount for the current operating condition (S10). The actual amount of air flowing into the combustion chamber from the mounted air flow sensor (AFS) is measured (S20).

Thereafter, the EGR control value is calculated in consideration of the temperature of the coolant and the correction value according to the degree of various loads on the vehicle (S30), and then the opening rate is controlled through the EGR solenoid valve.

At this time, the EGR valve is opened until the target air amount is followed based on the actual air amount, and the negative pressure generated in the engine is used as the actual working fluid related to the control of the EGR valve.

This method is known as the most accurate method at the moment because it controls the target air volume set in each operation area, but as pointed out in the above two methods, the actual EGR due to the effect of the deviation of the operation area and the single item deviation of the air flow sensor itself. The flow has a disadvantage that a lot of deviations between vehicles occur.

That is, the problems that may occur when using each of the above EGR control methods can be summarized as the following two things.

First, even when driving at the same speed due to the difference in frictional resistance and the difference in output between the vehicles, the driving region (engine rotation speed and fuel amount) shows a large difference.

Therefore, the target air volume set on the basis of the driving range shows a lot of difference even at the same speed. As a result, the difference in the EGR flow causes a difference in NOx, but it also increases the smoke, but increases the amount of smoke. There may be serious soot quality problems.

Secondly, since the air flow sensor is currently in mass production, there is a 20% variation between units, which inevitably causes a 20% variation in the EGR flow, which may cause a soot problem in a production vehicle. Will be formed.

In addition, by applying an expensive oxidation catalyst device and an EGR cooler device for stabilizing the exhaust gas in a diesel vehicle, it provides a rise in manufacturing cost, which also acts as a burden on the consumer.

The present invention has been invented to solve the above problems, and its object is to use a signal of a lambda sensor mounted on the exhaust side to detect the concentration of oxygen contained in the exhaust gas instead of an air flow sensor having a large mass deviation. By performing EGR feedback control to provide stability of the exhaust gas.

1 is a schematic block diagram of an exhaust gas recirculation control apparatus of a diesel vehicle according to the present invention;

2 is a flowchart of one embodiment for performing exhaust gas recirculation control in a diesel vehicle according to the present invention;

Figure 3 is a view showing the output characteristics compared to the intake air amount of the lambda sensor applied to the diesel vehicle according to the invention.

4 is a diagram illustrating output voltage characteristics of a lambda sensor applied to a diesel vehicle according to the present invention;

5 is a flowchart of an embodiment of performing exhaust gas recirculation control in a conventional diesel vehicle.

The present invention for realizing the above object and means for detecting the engine speed; Means for detecting a load change of the engine; Means for detecting a temperature of cooling water; A lambda sensor detecting a concentration of oxygen contained in the exhaust gas; An EGR valve for adjusting exhaust gas recirculation amount; The target lambda value for the EGR feedback control is set in consideration of the engine speed, the engine torque, and various correction variables, and the EGR valve is configured so that the amount of oxygen contained in the exhaust gas follows the target lambda value according to the signal detected from the lambda sensor. It characterized in that it comprises a control means for controlling the duty.

The present invention includes the steps of detecting a current operating condition in which engine start is maintained and setting a target lambda value for EGR feedback control; Calculating and setting an EGR control duty ratio according to a lambda value for implementing the set target lambda value; Detecting a signal of a lambda sensor, comparing the target lambda value with the set target lambda value, and calculating a feedback control duty ratio for following the target lambda value from the difference; And controlling the exhaust gas recirculation by controlling the EGR valve with the calculated feedback control duty ratio.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As can be seen in Figure 1, the exhaust gas recirculation control apparatus for a diesel vehicle according to the present invention is the engine speed detection unit 10, the engine load detection unit 20, the coolant temperature detection unit 30, lambda sensor 40, the control unit It consists of 50 and the EGR valve 60, the engine speed detection part 10 detects the current engine speed from the rotation speed of a crankshaft, and applies the information about it to the control part 50 side as a voltage value. .

The engine load detection unit 20 detects a load change of an engine that is changed according to on / off selection of an air conditioner, an equalizer, etc., driving of a power steering, etc., and applies the information about the load to the controller 50 as a voltage value. do.

The cooling water temperature detector 30 detects the temperature of the cooling water circulating in the cylinder block and applies the information about the cooling water to the controller 50 as a voltage value.

The lambda sensor 40 is mounted on the exhaust side, detects the concentration of oxygen contained in the exhaust gas, and applies information about the same to the controller 50 as a voltage value.

The lambda sensor 40 has an output characteristic proportional to the amount of intake air as shown in FIG.

In addition, as shown in Figure 4, evenly distributed and straightness to lambda 1 to 4, and has a low sensitivity output characteristics in the lambda 5 or more, but in the EGR region of a real diesel vehicle, because it is distributed within a maximum of 4 lambda lambda sensor There is no problem in the feedback control of the EGR through.

The controller 50 sets a target lambda value for the EGR feedback control in consideration of the detected engine speed, engine torque, and various correction variables, and the amount of oxygen included in the exhaust gas according to the signal detected from the lambda sensor 40. The EGR valve is controlled to follow this target lambda value.

The EGR valve 60 is driven according to the duty control signal applied from the control unit 50 to adjust the amount of recycle of the exhaust gas.

Referring to the operation of performing the exhaust gas recirculation control in the diesel vehicle according to the present invention including the function as described above are as follows.

When the engine of the diesel vehicle maintains the start-up, the control unit 50 detects the current operating state of the current engine speed, the degree of load on the engine, the temperature of the coolant, the engine torque, and the like (S101). A target lambda value for the EGR control is set for the current operation region according to the number and fuel amount, and a correction value according to the temperature condition and various load fluctuation conditions is set (S102).

Thereafter, the EGR control duty ratio according to the change in the lambda value for implementing the target lambda value is calculated and set (S103).

In the state where the EGR control duty ratio according to the change of the target lambda value and the lambda value is determined as described above, the controller 50 detects the voltage of the lambda sensor 40 which detects the oxygen concentration contained in the exhaust gas (S104). It compares with the target lambda value set in S102 (S105).

At this time, the feedback EGR duty ratio for following the target lambda value is calculated according to the difference detected from the compared result (S106), and the EGR solenoid valve 60 is controlled according to the calculated EGR duty ratio (S107). .

As described above, in the operation in which the EGR solenoid valve 60 is adjusted according to the EGR duty ratio, a target lambda value is detected by the above operation for each operation region, and a voltage value detected by feedback from the lambda sensor 40. Is repeated according to.

As described above, in the diesel vehicle according to the present invention, the EGR feedback control using the lambda sensor reduces the fluctuation of the exhaust gas, thereby eliminating overdesigned parts, thereby providing cost reduction.

In addition, the exhaust gas stabilization of the exhaust gas, which has been pointed out as a problem of the quality of diesel vehicles, is carried out precisely, thereby providing reliability of the vehicle by stabilizing the exhaust gas.

Claims (2)

Means for detecting engine speed; Means for detecting a load change of the engine; Means for detecting a temperature of cooling water; A lambda sensor detecting a concentration of oxygen contained in the exhaust gas; An EGR valve for adjusting exhaust gas recirculation amount; The target lambda value for the EGR feedback control is set in consideration of the engine speed, the engine torque, and various correction variables, and the EGR valve is configured so that the amount of oxygen contained in the exhaust gas follows the target lambda value according to the signal detected from the lambda sensor. The exhaust gas recirculation control apparatus of the diesel vehicle comprising a control means for controlling the duty. Setting a target lambda value for EGR feedback control by detecting a current operating condition in which engine start is maintained; Calculating and setting an EGR control duty ratio according to a lambda value for implementing the set target lambda value; Detecting a signal of a lambda sensor, comparing the target lambda value with the set target lambda value, and calculating a feedback control duty ratio for following the target lambda value from the difference; And controlling the exhaust gas recirculation by controlling the EGR valve based on the calculated feedback control duty ratio.