Method and apparatus for controlling EGR

Abstract

A method of controlling exhaust gas recirculation (EGR) for controlling recirculation of exhaust gas discharged from a combustion chamber of an engine includes: a data obtaining operation of obtaining data about an engine state and a gas supply state; a current EGR rate calculating operation of calculating a current EGR rate of supply gas based on the data; a demand EGR rate setting operation of setting a demand EGR rate matched with the data in a pre-made target EGR rate map; an error calculating operation of calculating a difference between the demand EGR rate and the current EGR rate; and a control operation of making the current EGR rate follow the demand EGR rate by changing a recirculation rate of the exhaust gas by adjusting an inhalation side pressure of the supply gas according to the difference.

Claims

1. A method of controlling exhaust gas recirculation (EGR) for controlling recirculation of exhaust gas discharged from a combustion chamber of an engine, the method comprising: a data obtaining operation of obtaining data about an operation state of the engine including rpm, a fuel supply quantity, and an inhalation air quantity of the engine; a current EGR rate calculating operation of calculating a current EGR rate of supply gas based on the data; a demand EGR rate setting operation of setting a demand EGR rate matched with the rpm and the fuel supply quantity in a pre-made target EGR rate map; an error calculating operation of calculating a difference between the demand EGR rate and the current EGR rate; and a control operation of making the current EGR rate follow the demand EGR rate by changing a recirculation rate of the exhaust gas by adjusting an inhalation side pressure of the supply gas according to the difference, wherein the current EGR rate is calculated based upon a difference between the inhalation air quantity and a non-EGR air quantity divided by the non-EGR air quantity, wherein the non-EGR air quantity is matched with the rpm in a pre-made non-EGR air quantity table, and wherein the control operation is performed by mutually adjusting an opening degree of an inhalation pressure control valve, which is provided at an inhalation side of the supply gas and adjusts an inhalation negative pressure, and an opening degree of an EGR valve, which is provided at a discharge side of the exhaust gas and introduces the exhaust gas to the inhalation side of the supply gas.

2. The method of claim 1, wherein the exhaust gas is introduced to the inhalation side of the supply gas along an EGR supply path branched from the discharge side of the exhaust gas, and the EGR supply path forms an independent loop that is not subordinate to auxiliary machinery.

3. The method of claim 1, wherein the control operation includes controlling the current EGR rate to satisfy the demand EGR rate by proportional-integral derivative (PID) control using an actual measurement value of an inhalation air quantity and the target EGR rate map.

4. An apparatus for controlling exhaust gas recirculation (EGR), the apparatus comprising: an engine including a speed sensor and an air flow meter; an actuator configured to control opening degrees of an inhalation pressure control valve and an EGR valve; and an engine control unit configured to obtain data about an operation state of the engine from the engine including rpm, a fuel supply quantity, and an inhalation air quantity of the engine, calculate an actual EGR rate and a demand EGR rate based on the obtained data and a pre made target EGR rate map, and transmit a control signal to the actuator when there is a difference between the actual EGR rate and the demand EGR rate as a result of the calculation, wherein the engine control unit makes a current EGR rate follow the demand EGR rate by changing a recirculation quantity of exhaust gas by adjusting a pressure of an inhalation side of supply gas according to the difference, wherein the current EGR rate is calculated based upon a difference between the inhalation air quantity and a non-EGR air quantity divided by the non-EGR air quantity, wherein the non-EGR air quantity is matched with the rpm in a pre-made non-EGR air quantity table, and wherein the engine control unit is configured to perform by mutually adjusting an opening degree of an inhalation pressure control valve, which is provided at an inhalation side of the supply gas and adjusts an inhalation negative pressure, and an opening degree of an EGR valve, which is provided at a discharge side of the exhaust gas and introduces the exhaust gas to the inhalation side of the supply gas.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram schematically illustrating a structure of an EGR control system according to an exemplary embodiment of the present disclosure.

(2) FIG. 2 is a diagram illustrating a concept of an EGR control logic according to the exemplary embodiment of the present disclosure.

(3) FIG. 3 is a flowchart illustrating the EGR control logic according to the exemplary embodiment of the present disclosure.

(4) FIG. 4 is a diagram illustrating a numerical value interpretation model of the EGR control system according to an exemplary embodiment of the present disclosure.

(5) FIG. 5 is a graph illustrating a result of the numerical value interpretation when a low-pressure EGR valve is solely used.

(6) FIG. 6 is a diagram illustrating a result of the numerical value interpretation when an opening degree of the low-pressure EGR valve and an opening degree of an IPCV are simultaneously controlled.

DETAILED DESCRIPTION

(7) Hereinafter, an exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

(8) FIG. 1 is a diagram schematically illustrating a structure of an exhaust gas recirculation (EGR) control system according to an exemplary embodiment of the present disclosure.

(9) Referring to FIG. 1, an EGR control system 100 according to an exemplary embodiment of the present disclosure includes an inhalation pressure control valve (IPCV) 5 installed at an inhalation manifold 2 side, which supplies external air sucked through a mass air flow meter (MAF) 8 and an air filter (A/F) 7 to a combustion chamber 1, and adjusting an inhalation negative pressure, and an EGR valve 6 installed in an EGR supply path 4 branched from an exhaust manifold 3 side, and introducing exhaust gas combusted in and discharged from the combustion chamber 1 to the inhalation manifold 2 side. The EGR valve 6 may be, for example, a low-pressure EGR valve (LP-EGR valve). Further, the EGR supply path 4 may form a lower pressure EGR loop (LP-EGR Loop) that is not subordinate to auxiliary machinery, such as a turbo charger.

(10) The EGR control system 100 of the present exemplary embodiment is characterized in that the adjustment of an EGR flow rate supplied to the combustion chamber 1 is not dependent on only the EGR valve 6, but a control range of the EGR is expanded to be larger than a limit (0 to 40%) in the related art by adjusting two variables including an opening degree (duty) of the EGR valve 6 and an opening degree of an inhalation pressure control valve 5.

(11) FIG. 2 is a diagram illustrating a concept of an EGR control logic according to the exemplary embodiment of the present disclosure.

(12) Referring to FIG. 2, an engine control unit (ECU) obtains measurement data about rpm, a fuel quantity (Fuel Q), and an air quantity (Air Q) of an engine from a speed sensor, an air flow meter, and the like provided in the engine (E/G), and calculates an actual EGR rate and a demand EGR rate based on the measurement data and an autonomously stored target EGR rate map. As a result of the calculation, when there is a difference between the actual EGR rate and the demand EGR rate, the ECU transmits a control signal to an actuator so as to make the actual EGR rate follow the demand EGR rate. Based on the control signal, the large quantity of EGR satisfying the demand EGR rate is supplied to the engine by adjusting the opening degree of the inhalation pressure control valve (IPCV) and the opening degree of the EGR valve (for example, the low-pressure EGR valve (LP-EGR valve)). Further, in order to perform accurate control in accordance with the demand EGR rate, proportional-integral-derivative (PID) control using an actual measurement value of an inhalation air quantity and the target EGR rate map may be performed.

(13) FIG. 3 is a flowchart illustrating the EGR control logic according to the exemplary embodiment of the present disclosure.

(14) Referring to FIG. 3, the engine control unit (ECU) obtains information, for example, current rpm information and actual fuel quantity (Fuel Q) information, based on which a target EGR rate or a demand EGR rate for low temperature combustion may be calculated, from the engine (S301).

(15) Next, the engine control unit (ECU) sets a demand EGR rate matched with the current rpm and the actual fuel quantity (Fuel Q) in the target EGR rate map which is prepared by a previous experiment in advance (S303).

(16) Table 1 below represents a target EGR rate map (%) according to the exemplary embodiment of the present disclosure.

(17) TABLE-US-00001 TABLE 1 RPM Fuel Q 800 1200 1600 2000 10 50 60 65 68 . . . . . . . . . . . . . . . 100  58 62 67 70

(18) Next, a current actual EGR rate is calculated based on a fresh air quantity (Air Q) measured by the flow meter and a non-EGR air Q table in the ECU (S305). Here, the actual EGR rate is a value obtained by subtracting the measurement value by the flow meter from the air rate calculated based on the non-EGR air quantity table, and is calculated by Equation 1 below.

(19) $\begin{array}{cc}\mathrm{Actual}\mathrm{EGR}\mathrm{Rate}\left[\%\right]=\frac{\begin{array}{c}\mathrm{Non}\mathrm{EGR}\mathrm{Air}\mathrm{Quantity}\left[\frac{\mathrm{kg}}{h}\right]-\\ \mathrm{Actual}\mathrm{Air}\mathrm{Quantity}\left[\frac{\mathrm{kg}}{h}\right]\end{array}}{\mathrm{Non}\mathrm{EGR}\mathrm{Air}\mathrm{Quantity}\left[\frac{\mathrm{kg}}{h}\right]}*100& \left[\mathrm{Equation}1\right]\end{array}$

(20) Table 2 represents the non-EGR air quantity table (kg/h) according to the exemplary embodiment of the present disclosure.

(21) TABLE-US-00002 TABLE 2 RPM 800 1200 1600 2000 Air Q 10 . . . . . . 800

(22) Next, a deviation is calculated by comparing the actual EGR rate calculated by the ECU and the demand EGR rate as expressed by Equation 2 (S307).
Deviation[%]=Demand EGRRate[%]−Actual EGR Rate[%]  [Equation 2]

(23) When there is a difference between the target EGR rate and the actual EGR rate, the actual EGR rate is made to follow the target EGR rate through the PID control by adjusting an opening degree of the low-pressure EGR valve (LP-EGR valve) and the opening degree of the inhalation pressure control valve (IPCV) (S309). That is, an inhalation negative pressure at the inhalation manifold side is adjusted by controlling the inhalation pressure control valve (IPCV), so that the large quantity of EGR satisfying the demand EGR rate is controlled to be introduced from the EGR valve side.

(24) Finally, when the actual EGR rate follows the target EGR rate, the PID control is terminated.

(25) FIG. 4 is a diagram illustrating a numerical value interpretation model of the EGR control system according to an exemplary embodiment of the present disclosure.

(26) A numerical value interpretation model was used to verify an effect of the EGR control according to the present disclosure. The 1-D interpretation model by Wave_Ricardo modeling with the “DL06” diesel engine, which satisfies the exhaust gas regulation standard of “Tier 4 Final” and was manufactured by the applicant, as a target was used as the numerical value interpretation model. Further, for comparison with the system in the related art, a result was separately analyzed when the low-pressure EGR valve was solely used and the inhalation pressure control valve and the low-pressure EGR valve were simultaneously used.

(27) When the low-pressure EGR valve is solely used, as illustrated in FIG. 5, it is shown that the EGR supply quantity reaches a limit at a level of about 30%.

(28) By contrast, when the low-pressure EGR valve is used together with the inhalation pressure control valve (IPCV), as illustrated in FIG. 6, it is shown that the EGR supply quantity satisfies up to 100% of the demand EGR rate according to an adjustment rate of the opening degrees of the IPCV and the low-pressure EGR valve.

(29) As described above, according to the EGR control of the present disclosure, there provides a remarkably improved effect in that it is possible to definitely solve a problem of the supply of the large quantity of EGR which has been a large obstacle in implementation and practical use of low temperature combustion.

(30) According to the aforementioned exemplary embodiment of the present disclosure, it is possible to expand a control range of an EGR rate by simultaneously adjusting opening degrees of the EGR valve and the inhalation pressure control valve (IPCV), thereby stably supplying the large EGR flow rate for implementing low temperature combustion. Particularly, the EGR rate of the EGR system in the related art has a limit of about 40%, but the EGR control system according to the present disclosure may sufficiently supply the EGR rate by up to 100%, thereby definitely solving an EGR supply problem.

(31) Further, the low-pressure EGR loop, which is not subordinate to auxiliary machinery, such as a turbo charger, is used, so that even though an operating point of the auxiliary machinery is changed, an EGR rate is not subordinately changed, thereby more accurately controlling the EGR Rate. Further, it is possible to accurately control an EGR rate through a control logic using only an inhalation air quantity measured by the flow meter, and it is also possible to perform accurate EGR control satisfying a demand EGR rate through the PID control using an actual measurement value of an inhalation air quantity and the target EGR rate map.

(32) The exemplary embodiments of the present disclosure have been described with reference to the accompanying drawings, but those skilled in the art will understand that the present disclosure may be implemented in another specific form without changing the technical spirit or an essential feature thereof.

(33) Accordingly, the exemplary embodiment described in the present specification is illustrative for all of the aspects, and it should not understand that the exemplary embodiment described in the present specification limits the present disclosure, and the scope of the present disclosure is defined by the claims to be described below, and it should be interpreted that all modifications or modified forms derived from the scope of the claims and an equivalent scope thereof are included in the scope of the present disclosure.