Method for controlling exhaust gas recirculation system for engine

Abstract

A method for controlling an exhaust gas recirculation (EGR) system which is provided with an intake throttle valve and an EGR valve driven by a motor may include detecting an engine speed and an amount of intake air for each cylinder of an engine while the engine is operating, determining an amount of air flow supplied to the engine based on the engine speed and the amount of intake air for each cylinder, determining an equivalent cross-section of the EGR valve based on the amount of air flow, determining an opening angle of the EGR valve based on the engine speed, the amount of intake air for each cylinder, the amount of air flow, and the equivalent cross-section of the EGR valve, and controlling the EGR valve according to the opening angle of the EGR valve.

Claims

1. A method for controlling an exhaust gas recirculation (EGR) system which is provided with an intake throttle valve and an EGR valve driven by a motor, the method comprising: detecting, by an engine controller, an engine speed and an amount of intake air for each cylinder of an engine while the engine is operating; determining, by the engine controller, an amount of air flow supplied to the engine based on the engine speed and the amount of intake air for each cylinder; determining, by the engine controller, an equivalent cross-section of the EGR valve based on an amount of an EGR gas passed through the EGR valve; determining, by the engine controller, an opening angle of the EGR valve based on the engine speed, the amount of intake air for each cylinder, the amount of air flow, and the equivalent cross-section of the EGR valve; and controlling, by the engine controller, the EGR valve according to the opening angle of the EGR valve, wherein the opening angle of the EGR valve is calculated through the following equation: =f.sub.2(A.sub.RED,M.sub.AIR,N), wherein A.sub.RED is an axis of the equivalent cross-section of the EGR valve, N is the engine speed, and M.sub.AIR is the amount of intake air for each cylinder, wherein the opening angle of the EGR valve is formed as a 3-dimensional map with respect to the equation for calculating the opening angle of the EGR valve, and wherein the 3-dimensional map includes an axis of the engine speed, an axis of the amount of intake air for each cylinder of the engine, and the axis of the equivalent cross-section of the EGR valve.

2. The method of claim 1, wherein the amount of air flow is determined through the following equation: ${\stackrel{.}{m}}_{\mathrm{AIR}}=\frac{n}{2}\frac{2N}{60}{M}_{\mathrm{AIR}},$ wherein {dot over (m)}.sub.AIR is the amount of air flow, n is a number of cylinders of the engine, N is the engine speed, and M.sub.AIR is the amount of intake air for each cylinder.

3. The method of claim 1, wherein the equivalent cross-section of the EGR valve is determined through the following equation: $A_{\mathrm{RED}}=\frac{{\stackrel{.}{m}}_{\mathrm{EGR}}}{\sqrt{\frac{2}{\left(-1\right){\mathrm{RT}}_{\mathrm{EGRV}}}}{P}_{\mathrm{EGRV}}{}_{\mathrm{EGR}}},$ and wherein: A.sub.RED is the equivalent cross-section of the EGR valve, ${}_{\mathrm{EGR}}=\{\begin{array}{c}\sqrt{{\left(\frac{P_{\mathrm{COMP}}}{P_{\mathrm{EGRV}}}\right)}^{\frac{2}{}}-{\left(\frac{P_{\mathrm{COMP}}}{P_{\mathrm{EGRV}}}\right)}^{\frac{+1}{}}},\frac{P_{\mathrm{COMP}}}{P_{\mathrm{EGRV}}}>0.52\\ 0.2588,\frac{P_{\mathrm{COMP}}}{P_{\mathrm{EGRV}}}<0.52\end{array},$ is a specific heat ratio, R is a gas constant of the EGR gas, P.sub.EGRV is a front pressure of the EGR valve, P.sub.COMP is a rear pressure of the EGR valve, and T.sub.EGRV is a temperature of the EGR gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram illustrating a typical exhaust gas recirculation (EGR) system which controls an intake throttle valve and an EGR valve using one motor according to the related art.

(2) FIG. 2 is a graph for explaining a drawback of a method for controlling an EGR system according to the related art.

(3) FIG. 3 is a block diagram for implementing an exemplary method for controlling an EGR system according to the present invention.

(4) FIG. 4 is a flowchart of an exemplary method for controlling an EGR system according to the present invention.

(5) FIG. 5 is a 3-dimensional map formed by an exemplary method for controlling an EGR system according to the present invention.

(6) It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

DETAILED DESCRIPTION

(7) Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

(8) FIG. 3 is a block diagram of a system for implementing a method for controlling an EGR system according to various embodiments of the present invention.

(9) Referring to FIG. 3, the system for implementing the method for controlling the EGR system according to various embodiments of the present invention may include an EGR controller 100 configured to control general operation of the EGR system; an EGR sensor 50 configured to detect whether EGR is performed, and an air flow sensor 60 configured to detect an amount of air. In the system, an EGR valve 20 and an intake throttle valve 10 are controlled by one motor 30.

(10) The motor 30, the EGR valve 20, the intake throttle valve 10, the EGR sensor 50, and the air flow sensor 60 may be similar to those shown in FIG. 1 or may be those typically applied in the conventional art.

(11) The EGR controller 100 may be one or more microprocessors and/or hardware including a microprocessor that can be operated by a predetermined program, wherein the predetermined program may include a series of commands for executing the method for controlling the EGR system to be described later according to various embodiments of the present invention.

(12) The EGR controller 100 may be included in an engine electronic control unit (ECU) 11 configured to control an engine 1 as shown in FIG. 3, or may include the ECU 11.

(13) Hereinafter, a method for controlling an EGR system according to various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(14) FIG. 4 is a flowchart of a method for controlling an EGR system according to various embodiments of the present invention.

(15) Referring to FIG. 4, the EGR controller 100 determines whether the engine 1 is operating (S100). While the engine 1 is operating, the EGR controller 100 performs EGR control.

(16) The operation of the engine 1 may be detected or determined through signals outputted from the ECU 11, as is well-known to a person skilled in the art.

(17) When the operation of the engine 1 is detected or determined at step S100, the EGR controller 100 detects an engine speed (N) of the engine 1 and an amount (M.sub.AIR) of intake air for each cylinder of the engine 1 (S200).

(18) The engine speed (N) may be detected or determined through the ECU 11, and the amount (M.sub.AIR) of intake air for each cylinder may be detected or determined by the air flow sensor 60 and/or through the ECU 11.

(19) When the engine speed (N) and the amount (M.sub.AIR) of intake air for each cylinder is detected, the EGR controller 100 calculates an amount ({dot over (m)}.sub.AIR) of air flow supplied to the engine 1 based on the engine speed (N) and the amount (M.sub.AIR) of intake air for each cylinder (S300). For example, the amount ({dot over (m)}.sub.AIR) of air flow may be calculated through the following equation.

(20) ${\stackrel{.}{m}}_{\mathrm{AIR}}=\frac{n}{2}\frac{2N}{60}{M}_{\mathrm{AIR}}$
(where n is the number of cylinders of the engine)

(21) When the amount ({dot over (m)}.sub.AIR) of air flow is calculated, the EGR controller 100 calculates an equivalent cross-section (A.sub.RED) of the EGR valve 20 based on the amount ({dot over (m)}.sub.AIR) of air flow (S400). For example, the equivalent cross-section (A.sub.RED) may be calculated through the following equation.

(22) $A_{\mathrm{RED}}=\frac{{\stackrel{.}{m}}_{\mathrm{EGR}}}{\sqrt{\frac{2}{\left(-1\right){\mathrm{RT}}_{\mathrm{EGRV}}}}{P}_{\mathrm{EGRV}}{}_{\mathrm{EGR}}}$${}_{\mathrm{EGR}}=\{\begin{array}{c}\sqrt{{\left(\frac{P_{\mathrm{COMP}}}{P_{\mathrm{EGRV}}}\right)}^{\frac{2}{}}-{\left(\frac{P_{\mathrm{COMP}}}{P_{\mathrm{EGRV}}}\right)}^{\frac{+1}{}}},\frac{P_{\mathrm{COMP}}}{P_{\mathrm{EGRV}}}>0.52\\ 0.2588,\frac{P_{\mathrm{COMP}}}{P_{\mathrm{EGRV}}}<0.52\end{array}$

(23) (where is the specific heat ratio, R is a gas constant of the EGR gas, P.sub.EGRV is a front pressure of the EGR valve, P.sub.COMP is a rear pressure of the EGR valve, and T.sub.EGRV is a temperature of the EGR gas)

(24) When the equivalent cross-section (A.sub.RED) is calculated, the EGR controller 100 calculates an opening angle () of the EGR valve 20 through the following equation based on the engine speed (N), the amount (M.sub.AIR) of intake air for each cylinder, the amount ({dot over (m)}.sub.AIR) of air flow, and the equivalent cross-section (A.sub.RED) of the EGR valve 20 (S500), and then controls the EGR valve 20 according to the calculated opening angle () of the EGR valve 20 (S600).
=f.sub.1(A.sub.RED,{dot over (m)}.sub.AIR(N,M.sub.AIR),N)=f.sub.2(A.sub.RED,M.sub.AIR,N).

(25) As shown in FIG. 5, the opening angle () of the EGR valve 20 may be formed as a 3-dimensional orthogonal map with respect to the equation for calculating the opening angle () of the EGR valve 20, wherein the 3-dimensional orthogonal map may have an axis of the engine speed (N), an axis of the amount (M.sub.AIR) of intake air for each cylinder of the engine 1, and an axis of the equivalent cross-section (A.sub.RED) of the EGR valve 20.

(26) The 3-dimensional orthogonal map may be formed with respect to every predetermined engine speed to accurately set values of the opening angle of the EGR valve 20.

(27) Accordingly, according to various embodiments of the present invention, it is possible to accurately monitor and calculate complex flow of EGR gas by forming and applying a formula to form a 3-dimensional map based on an equivalent orthogonal cross-section, an amount of intake air for each cylinder, and an engine speed in an EGR system which controls an intake throttle valve and an EGR valve using one motor, thereby improving control stability and reliability for the engine.

(28) The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.