JP6579081B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine.

  Japanese Unexamined Patent Application Publication No. 2008-175101 discloses an exhaust gas recirculation device for an internal combustion engine. This conventional apparatus includes an EGR pipe connecting an exhaust pipe and an intake pipe, a water-cooled EGR cooler provided on the exhaust pipe side of the EGR pipe, and an EGR valve provided on the intake pipe side of the EGR pipe. I have. This conventional device also branches from the EGR pipe in the middle of the EGR pipe, bypasses the EGR cooler, and joins the bypass pipe joining the EGR pipe between the EGR cooler and the EGR valve, and the EGR pipe of the bypass pipe. And a bypass valve provided in the section. The bypass valve has a variable flow area of one of an EGR pipe (hereinafter also referred to as a “first branch pipe”) and a bypass pipe (hereinafter also referred to as a “second branch pipe”) provided with an EGR cooler, and the other. It is configured to open.

  In this conventional apparatus, the opening degree of the bypass valve is controlled. Since the EGR cooler is provided in the first branch pipe, the amount of heat released from the EGR gas flowing through the first branch pipe is different from the amount of heat released from the EGR gas flowing through the second branch pipe. Therefore, when the opening degree control of the bypass valve is performed, it is possible to adjust the temperature of the EGR gas flowing on the intake pipe side from the merging portion of the EGR pipe and the temperature of the intake air merged with the EGR gas.

JP 2008-175101 A JP 2009-121358 A JP 2006-066544 A

  However, Japanese Patent Laid-Open No. 2008-175101 does not consider that the amount of heat released from the EGR gas flowing through the first and second branch pipes depends on the flow rate of the EGR gas flowing through each pipe. Further, it is not considered that the temperature of the EGR gas in the central part of the first and second branch pipes depends on the internal pressure of these pipes. Therefore, the following problems may occur in the opening degree control in the conventional apparatus. That is, the temperature of the EGR gas flowing through these pipes changes with the change in the flow rate of the EGR gas flowing through the first and second branch pipes and the pressure in the pipe. As a result, the adjustment of the opening degree of the bypass valve is repeated, and there is a possibility that it takes time to converge the temperature of the EGR gas flowing on the intake pipe side from the merging portion of the EGR pipe.

  The present invention has been made in view of the above-described problems. That is, in an exhaust gas recirculation apparatus for an internal combustion engine that includes a bypass pipe that branches from the EGR pipe and bypasses the EGR cooler and merges with the EGR pipe, the convergence of the temperature of the EGR gas that flows on the intake pipe side from the joining portion of the EGR pipe The purpose is to increase.

The present invention is an exhaust gas recirculation device for an internal combustion engine for solving the above problems,
An EGR pipe connecting the exhaust pipe and the intake pipe;
A water-cooled EGR cooler provided on the exhaust pipe side of the EGR pipe;
A bypass pipe that branches from the EGR pipe in the middle of the EGR pipe, bypasses the EGR cooler, and joins the EGR pipe;
A control valve that changes a flow rate ratio that is a ratio of a flow rate of the EGR gas flowing through the EGR cooler to a total flow rate of the EGR gas flowing through the EGR pipe;
Control means for controlling the opening degree of the control valve based on a target value of the flow rate ratio that causes the temperature of EGR gas flowing on the intake side of the EGR pipe to join with the bypass pipe to follow the target value;
Calculation that calculates one of the solutions of the quadratic expression as a target value of the flow rate ratio when an energy balance formula that is established with respect to the energy of the EGR gas before and after merging at the merging portion is expressed by the quadratic expression of the flow rate ratio The coefficient of the quadratic expression includes a slope and intercept of the first linear function and a slope and intercept of the second linear function, and the first linear function is A linear approximation of the relationship between the cooling efficiency in the EGR cooler and the first division value, with the first division value obtained by dividing the flow rate of the EGR gas flowing through the EGR cooler by the exhaust temperature as a variable. The second linear function is a function of a cooling efficiency in the bypass pipe and a variable of a second divided value obtained by dividing the flow rate of the EGR gas flowing through the bypass pipe by the exhaust temperature. For each interval in which the relationship with the divide value is linearly approximated A calculation means is a first-order function was similar,
It is characterized by providing.

  According to the present invention, the energy balance equation that is established with respect to the energy of the EGR gas before and after merging at the merging portion is expressed by the ratio of the flow rate of the EGR gas flowing through the EGR cooler to the total flow rate of the EGR gas flowing through the EGR pipe It can be expressed by a quadratic expression. The coefficients of this quadratic expression include the slope and intercept of a linear function that linearly approximates the relationship between the cooling efficiency in the EGR cooler and the first divided value, with the first divided value as a variable, and the second divided value. And the slope and intercept of a linear function approximated for each interval in which the relationship between the cooling efficiency in the bypass pipe and the second divided value is linearly approximated. Here, the first division value is a value obtained by dividing the flow rate of EGR gas flowing through the EGR cooler by the exhaust temperature, and the second division value is obtained by dividing the flow rate of EGR gas flowing through the bypass pipe by the exhaust temperature. Is the value obtained. Therefore, according to the present invention, the flow rate of the EGR gas flowing through the EGR cooler and the bypass pipe can be taken into account when calculating the target value of the flow rate ratio. In addition, according to the present invention, one of the solutions of the quadratic equation can be calculated as the target value of the flow rate ratio. Therefore, even when the flow rate of the EGR gas flowing through the EGR cooler or the bypass pipe is changed, one of the solutions of the quadratic equation can be immediately calculated as the optimum solution of the target value of the flow rate ratio. Therefore, according to the present invention, the temperature of the EGR gas flowing on the intake side from the junction with the bypass pipe can be made to follow the target value in a short time.

It is a figure explaining the structural example of the system which concerns on embodiment of this invention. It is a figure explaining the problem in the general opening degree control of the control valve 22 shown in FIG. It is a figure explaining the problem in the general opening degree control of the control valve 22 shown in FIG. It is a figure which shows an example of the relationship between value TegrC / T4 and cooling efficiency (eta) c, and the relationship between value TegrCbp / T4 and cooling efficiency (eta) cbp. In an embodiment of the invention, it is a figure showing an example of a processing routine which ECU30 performs. It is a figure explaining the structural example of the other system which can apply this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

[Description of system configuration]
FIG. 1 is a diagram illustrating a configuration example of a system according to an embodiment of the present invention. A system 10 shown in FIG. 1 is an engine system mounted on a vehicle and includes an EGR pipe 12. The EGR pipe 12 constitutes a part of an EGR device that recirculates exhaust gas flowing through an engine exhaust pipe (not shown) to the intake pipe 14. The EGR device includes, in addition to the EGR pipe 12, a water-cooled EGR cooler 16 that cools exhaust gas (EGR gas) flowing through the EGR pipe 12 with cooling water, and a bypass pipe 18 that bypasses the EGR cooler 16. Yes. The EGR device further includes a control valve 22 made of an electromagnetic valve or the like at the junction 20 where the bypass pipe 18 joins the EGR pipe 12. In addition, the structure of the engine applied to this invention is not specifically limited.

The control valve 22 is a flow rate ratio R of the flow rate GegrC of EGR gas flowing between the EGR cooler 16 and the merging portion 20 to the total flow rate Gegr of EGR gas flowing through the EGR pipe 12 (however, the flow rate ratio R is 0 ≦ R ≦ 1). Is configured to change. In the present embodiment, the flow rate ratio R uses the total flow rate Gegr as the sum of the flow rate GegrC of the EGR gas flowing between the EGR cooler 16 and the merging portion 20 and the flow rate GegrCbp of the EGR gas flowing through the bypass pipe 18. It is represented by the following formula (1).
R = GegrC / Gegr
= GegrC / (GegrC + GegrCbp) (1)
When the total flow rate Gegr and the flow rate GegrCbp are used, the above formula (1) is expressed by the following formula (2).
GegrCbp = (1-R) · Gegr (2)

  The system 10 shown in FIG. 1 further includes an EGR valve 24 made of an electromagnetic valve or the like on the intake pipe 14 side of the control valve 22 of the EGR pipe 12. The EGR valve 24 together with the EGR pipe 12, the EGR cooler 16, the bypass pipe 18 and the control valve 22 constitutes a part of the EGR device. The EGR valve 24 is configured to change the ratio (EGR rate) of the EGR gas that is recirculated to the cylinder of the internal combustion engine via the EGR pipe 12 in the entire intake air. In the state where the EGR valve 24 is fully closed, the EGR pipe 12 is shut off and the EGR rate becomes zero.

  The system 10 shown in FIG. 1 also includes an ECU (Electronic Control Unit) 30 as a control device. The ECU 30 includes a RAM (random access memory), a ROM (read only memory), a CPU (microprocessor), and the like. The ECU 30 captures and processes signals from various sensors mounted on the vehicle accompanying the system 10. Various sensors include an air flow meter that detects the intake air amount Ga, an atmospheric temperature sensor that detects the atmospheric temperature tha, a water temperature sensor that detects the water temperature thw of the cooling water flowing through the EGR cooler 16, and an exhaust gas temperature T4 that flows through the exhaust pipe. An exhaust temperature sensor is included. ECU30 processes the signal of each taken-in sensor, and operates various actuators according to a predetermined control program. The actuator operated by the ECU 30 includes the control valve 22 and the EGR valve 24 described above.

[Description of Control of Embodiment]
Before describing the control of the present embodiment, general opening degree control of the control valve 22 shown in FIG. 1 will be described with reference to FIGS. This general opening degree control is positioned as a comparative example of control according to the present embodiment described later. In the control according to this comparative example (hereinafter also referred to as “comparison control”), the next step is to make the temperature Tegr of the EGR gas flowing between the control valve 22 and the EGR valve 24 shown in FIG. The flow rate ratio R is calculated by S1 to S4.
Step S1: Estimation of current flow rate GegrC and flow rate GegrCbp Step S2: Prediction of heat exchange amount in EGR cooler 16 and heat exchange amount in bypass pipe 18 Step S3: EGR gas flowing between EGR cooler 16 and junction 20 Of the EGR gas flowing through the bypass pipe 18 and the temperature TegrCbp of the EGR gas Step S4: Calculation of the flow rate ratio R based on an equation (energy balance equation) that holds for the energy of the EGR gas upstream and downstream of the junction 20

  It is assumed that the flow rate of the cooling water flowing through the EGR cooler 16 during the comparative control is maintained at a sufficient amount. FIG. 2 is a diagram for explaining a problem in the comparison control. The upper part of FIG. 2 shows the EGR upstream gas temperature and the total EGR passing gas amount during the comparison control. This “EGR upstream gas temperature” means the temperature of the EGR gas immediately after flowing into the EGR pipe 12 shown in FIG. 1, and corresponds to the exhaust temperature T4 described above. The “total EGR passage gas amount” means the total flow rate of the EGR gas immediately after flowing into the EGR pipe 12 shown in FIG. 1, and corresponds to the above-described total flow rate Gegr.

  In the middle part of FIG. 2, the EGR downstream gas temperature during the comparative control and its target temperature are depicted. This “EGR downstream gas temperature” means the temperature of the EGR gas after merging in the merging portion 20 shown in FIG. 1, and corresponds to the above-described temperature Tegr. In the lower part of FIG. 2, the cooler gas temperature, the bypass gas temperature, and the cooler ratio (diversion ratio) during comparison control are depicted. The “cooler gas temperature” means the temperature TegrC estimated in step S3 described above. The “bypass gas temperature” means the temperature TegrCbp estimated in step S3. The “cooler ratio (diversion ratio)” means the flow rate ratio R calculated in step S4 described above.

As shown in the upper part of FIG. 2, the EGR upstream gas temperature is kept constant. On the other hand, the total EGR passage gas amount is divided into three periods that are kept constant. This total EGR passing gas amount was kept constant during the period from time t ₀ to time t ₁ is, because that is stepwise increased at time t ₁ and time t _2. The reason why the total EGR passage gas amount is increased stepwise at time t ₁ and time t ₂ is that the opening degree of the EGR valve 24 is increased in accordance with the request to increase the EGR rate. The opening degree control of the EGR valve 24 is performed in the ECU 30 separately from the processes in steps S1 to S4 described above.

As shown in the lower part of FIG. 2, the cooler ratio rapidly increases immediately after time t ₀ , time t _1, and time t ₂ . The cooler ratio rises rapidly immediately after time t _0, it cooler ratio is zero at time t _0, the flow rate ratio R to start the introduction of the EGR gas into the EGR cooler 16, the above steps S1~ This is because it was calculated through the process of S4. The cooler ratio immediately after time t ₁ and time t ₂ rises rapidly is because total EGR passing gas amount at time t ₁ and time t ₂ is rapidly increased. If the total EGR passage gas amount is rapidly increased, the value of the flow rate ratio R calculated through the processing of steps S1 to S4 described above also greatly increases.

Here, the period (A) immediately after time t ₀ shown in FIG. 2 represents the time required for the EGR downstream gas temperature to converge to the target value. This is due to the following problem. That is, the heat exchange amount in the EGR cooler 16 and the bypass pipe 18 depends on the flow rate of the EGR gas flowing through them. In addition, the temperature of the EGR gas flowing through the central portions of the EGR cooler 16 and the bypass pipe 18 changes at a speed equivalent to the change speed of these internal pressures. Therefore, if the opening degree of the control valve 22 is changed based on the flow rate ratio R calculated through the above-described steps S1 to S4, the estimated values of the temperature TegrC and the temperature TegrCbp estimated in step S3 change. Therefore, the processing of steps S1 to S4 is repeated, and the EGR downstream gas temperature does not readily converge to the target value. In other words, the optimum solution of the flow rate ratio R cannot be reached by a single process of steps S1 to S4.

Further, in the period immediately after time t ₂ shown in FIG. 2 (B), the cooler ratio has gone hunting not stabilized. This is due to the following problem. That is, when the bypass gas temperature shown in the lower part of FIG. 2 is higher than the cooler gas temperature and the temperature Tegr shown in the middle part of the figure is higher than the target value, the EGR downstream gas temperature is lowered by increasing the cooler ratio. It should be. However, by enhanced cooler ratio lowers the value of the bypass gas temperature estimated in step S3 described above, falls below the Kuragasu temperature at time t _3. However, in the time t _3, the temperature Tegr shown in the middle part of FIG. 2 remains higher than the target value. Then, theoretically, in order to lower the temperature Tegr, it is sufficient to use a relatively low bypass gas temperature, so the value of the flow rate ratio R calculated through the processing of steps S1 to S4 becomes small. In other words, the time t ₃ or later become lowered cooler ratio.

The decrease in the cooler ratio means that the flow rate GegrCbp of the EGR gas flowing through the bypass pipe 18 shown in FIG. 1 increases. Here, the bypass pipe 18 shown in FIG. 1 is not provided with a heat exchanger such as the EGR cooler 16, and it is the outside air that exchanges heat with the EGR gas flowing through the bypass pipe 18. Therefore, if the flow rate GegrCbp of the EGR gas increases, the bypass gas temperature will start to rise soon. Thus, the bypass gas temperature shown in the lower part of FIG. 2, at time t ₄ immediately after time t _3, will exceed the Kuragasu temperature. However, even in this time t _4, the temperature Tegr shown in the middle part of FIG. 2 remains higher than the target value. Then, theoretically, it is sufficient to use a relatively low cooler gas temperature. Therefore, the time t ₄ and later, so that the cooler ratio rises. As described above, when the temperature Tegr shown in the middle of FIG. 2 continues to be higher than the target value, the cooler ratio hunts.

The hunting of the cooler ratio is caused by lowering the cooler ratio in spite of the fact that the cooler ratio should be kept at a high value. However, if the temperature Tegr continues to be higher than the target value despite keeping the cooler ratio at a high value, another problem may occur. FIG. 3 illustrates this problem. If the cooler ratio is kept at a high value, as shown in the middle part of FIG. 3, the bypass temperature is lowered and greatly falls below the cooler gas temperature. Under such circumstances, when the temperature Tegr is far below the target value changes rapidly at the time t _5, theoretically, it becomes that may be utilized relatively high Kuragasu temperatures. In other words, it determines that may be utilized relatively high Kuragasu temperature in EGR gas despite possible elevated temperature Tegr in short time resulting in increasing the time t ₅ to flow to the bypass pipe 18 shown in FIG. 1 As a result, the cooler ratio does not decrease at all.

In consideration of the problems in the comparative control described above, in the control according to the present embodiment, the following equation (a linear approximation of the relationship between the value obtained by dividing the temperature Tegr by the exhaust temperature T4 and the cooling efficiency ηc in the EGR cooler 16) 3) and the flow rate ratio R is calculated using the following equation (4) that linearly approximates the relationship between the value obtained by dividing the temperature Tegr by the exhaust temperature T4 and the cooling efficiency ηcbp in the bypass pipe 18.
ηc = α · GegrC / T4 + β (3)
ηcbp = γ · GegrCbp / T4 + ε (4)
In the above equations (3) and (4), α, β, γ and ε are coefficients. In the present embodiment, coefficient α and coefficient β are stored in the ROM or RAM of ECU 30 as a map associated with flow rate GegrC / T4, and coefficient γ and coefficient ε are stored as a map associated with flow rate GegrCbp / T4, respectively. And

  First, linear approximation of the above two relationships will be described with reference to FIG. FIG. 4 is a diagram illustrating an example of the relationship between the value TegrC / T4 and the cooling efficiency ηc, and the relationship between the value TegrCbp / T4 and the cooling efficiency ηcbp. As shown in the upper part of FIG. 4, the relationship between the value TegrC / T4 and the cooling efficiency ηc can be approximated linearly. This is because the flow rate of the cooling water flowing through the EGR cooler 16 is kept at a sufficient amount. The coefficient α and coefficient β in the above equation (3) can be calculated as the slope and intercept of the linear function shown in the upper part of FIG.

On the other hand, the relationship between the value TegrCbp / T4 and the cooling efficiency ηcbp cannot be approximated linearly. However, if the relationship between the value TegrCbp / T4 and the cooling efficiency ηcbp is divided by intervals I _{1 to} I ₄ that can be linearly approximated, this relationship can be approximated linearly at each interval. The above equation (4) is an equation representing the relationship between the value TegrCbp / T4 and the cooling efficiency ηcbp when the value TegrCbp / T4 is divided by such intervals I _{1 to} I ₄ . The coefficient γ and the coefficient ε in the equation (4) can be calculated for each section as the slope and intercept of the linear function approximated for each section of the value TegrCbp / T4 shown in the lower part of FIG.

In the control according to the present embodiment, a secondary obtained by substituting the above equations (3) and (4) into an equation (energy balance equation) that holds for the energy of the EGR gas upstream and downstream of the merging section 20. The flow rate ratio R is calculated by solving the equation. First, the energy balance type will be described. The energy balance equation is an equation showing that the energy Eegr of the EGR gas downstream of the merging portion 20 is equal to the energy of the EGR gas upstream of the merging portion 20. Specifically, the energy balance equation is expressed by the following equation (5) using the energy Ec of the EGR gas flowing between the EGR cooler 16 and the junction 20 and the energy Ecbp of the EGR gas flowing through the bypass pipe 18. The
Eegr = Ec + Ecbp (5)

When the above equation (5) is modified by focusing on the temperature of the EGR gas and the flow rate ratio R, the following equation (6) is derived.
(5) ⇔Tegr = R · TegrC + (1-R) · Tegrcbp
⇔Tegr = R · {T4- (T4-thw) · ηc} + (1-R) · {T4- (T4-tha) · ηcbp} (6)

Substituting the following formulas (7) and (8) into the above formula (6) and arranging them by the flow rate ratio R, the following formula (9) is derived. The following formulas (7) and (8) are based on the above formulas (1) and (2), and GegrC / T4 and GegrCbp / T4 which are variables of the above formulas (3) and (4) are both Gegr. / T4.
ηc = α · R · Gegr / T4 + β (7)
ηcbp = γ · (1-R) · Gegr / T4 + ε (8)
0 = {(T4w · α + T4a · γ) · Gegr / T4} · R ²
+ {− 2 · T4a · γ · Gegr / T4 + (T4w · β−T4a · ε)} · R
+ (T4a · γ · Gegr / T4 + T4a · ε-T4e) (9)
However, in Equation (9), T4a = T4-tha, T4w = T4-thw, and T4e = T4-Tegr.

  Since the above equation (9) is a quadratic equation of the flow rate ratio R, one of the solutions (R1, R2) of this quadratic equation is an optimal solution of the flow rate ratio R that causes the temperature Tegr to follow the target value. I can say that. If one of the solutions (R1, R2) R1 is R1 <0 or R1> 1, the solution R1 does not satisfy the precondition of the flow rate ratio R. Determine to be the optimal solution. As described above, according to the control according to the present embodiment, it is possible to reach the optimal solution for the flow rate ratio R at a time without performing the above-described steps S1 to S4. That is, it is possible to converge the temperature Tegr to the target value in a short time while avoiding the occurrence of the problems described in FIG. 2 and FIG.

  FIG. 5 is a diagram illustrating an example of a processing routine executed by the ECU 30 in the present embodiment. This processing routine is executed every predetermined control cycle (for example, every combustion cycle of a cylinder included in the engine).

  In the routine shown in FIG. 5, first, the total flow rate Gegr, temperature Tegr, exhaust temperature T4, water temperature thw, atmospheric temperature tha, intake air amount Ga, etc. are acquired (step S10). In step S10, the total flow rate Gegr is estimated based on, for example, the intake air amount Ga detected by the air flow meter and the current value of the EGR rate. The total flow rate Gegr may be detected by a sensor separately provided in the EGR pipe 12. The total flow rate Gegr at the time of engine start is set to zero. For example, the previous value of the target value of the temperature Tegr is acquired as the temperature Tegr. Note that the “previous value of the target value of the temperature Tegr” refers to the target value of the temperature Tegr that was set when the ECU 30 last executed this processing routine. Further, the exhaust temperature T4, the water temperature thw, and the atmospheric temperature tha are detected by the sensors described above.

  Subsequent to step S10, the required diversion ratio is calculated (step S12). This “required diversion ratio” means a target value of the flow rate ratio R necessary for causing the temperature Tegr to follow the target value. In step S12, the required diversion ratio is calculated as follows, for example. First, the coefficient α, the coefficient β, the coefficient γ, and the coefficient ε are specified based on the total EGR passing gas amount acquired in step S10 and the map stored in the ECU 30. Then, the specified coefficient α, coefficient β, coefficient γ, coefficient ε, and the parameter acquired in step S10 are substituted into the solution formula of the above equation (9). Thereby, the required diversion ratio (that is, the flow rate ratio R) is calculated. As the first condition of the flow rate ratio R, when the total flow rate Gegr is zero, the flow rate ratio R is set to zero regardless of the values of the quadratic solutions (R1, R2). Further, as the second condition, when the values in the square root of the quadratic solution (R1, R2) are all negative, the flow rate ratio R is set to 1 regardless of the value of the solution (R1, R2).

  Subsequent to step S12, the valve opening is calculated (step S14). This “valve opening” is the opening of the control valve 22. In step S14, the opening degree of the control valve 22 that realizes the flow rate ratio R is calculated and input to the control valve 22 as a command value.

  As described above, according to the processing routine shown in FIG. 5, it is possible to reach the optimal solution for the flow rate ratio R at a time without performing the above-described steps S <b> 1 to S <b> 4 performed in the comparison control. That is, it is possible to converge the temperature Tegr to the target value in a short time while avoiding the occurrence of the problems described in FIG. 2 and FIG.

In the above-described embodiment, the “control means” of the present invention is realized by the ECU 30 executing the process of step S14 in FIG. 5, and the ECU 30 executes the process of step S12 in FIG. The “calculation means” of the invention is realized.
In the above-described embodiment, the above equation (9) corresponds to the “secondary expression of the flow rate ratio” of the present invention, and the coefficient α and the coefficient β of the above equation (3) are the “first” Corresponding to “Slope and intercept of linear function”, coefficient γ and coefficient ε in the above equation (4) correspond to “Slope and intercept of second linear function” of the present invention.

  By the way, in the above-mentioned embodiment, it demonstrated on the premise of the opening degree control of the control valve 22 of the system 10 shown in FIG. However, the present invention can also be applied to the system shown in FIG. FIG. 6 is a diagram for explaining a configuration example of another system to which the present invention is applicable. A system 40 shown in FIG. 6 is an engine system mounted on a vehicle, like the system 10 shown in FIG. The system 40 includes a control valve 26 provided in the EGR pipe 12 between the EGR cooler 16 and the merging portion 20, and a control valve 28 provided in the bypass pipe 18. When the present invention is applied to the system 40, the flow rate ratio R calculated from the above equation (9) may be realized by cooperative control of the control valves 26 and 28.

10,40 system (engine system)
12 EGR pipe 14 Intake pipe 16 EGR cooler 18 Bypass pipe 20 Junction section 22, 26, 28 Control valve 24 EGR valve 30 ECU

Claims (1)

An EGR pipe connecting the exhaust pipe and the intake pipe;
A water-cooled EGR cooler provided on the exhaust pipe side of the EGR pipe;
A bypass pipe that branches from the EGR pipe in the middle of the EGR pipe, bypasses the EGR cooler, and joins the EGR pipe;
A control valve that changes a flow rate ratio that is a ratio of a flow rate of the EGR gas flowing through the EGR cooler to a total flow rate of the EGR gas flowing through the EGR pipe;
Control means for controlling the opening degree of the control valve based on a target value of the flow rate ratio that causes the temperature of EGR gas flowing on the intake side of the EGR pipe to join with the bypass pipe to follow the target value;
Calculation that calculates one of the solutions of the quadratic expression as a target value of the flow rate ratio when an energy balance formula that is established with respect to the energy of the EGR gas before and after merging at the merging portion is expressed by the quadratic expression of the flow rate ratio The coefficient of the quadratic expression includes a slope and intercept of the first linear function and a slope and intercept of the second linear function, and the first linear function is A linear approximation of the relationship between the cooling efficiency in the EGR cooler and the first division value, with the first division value obtained by dividing the flow rate of the EGR gas flowing through the EGR cooler by the exhaust temperature as a variable. The second linear function is a function of a cooling efficiency in the bypass pipe and a variable of a second divided value obtained by dividing the flow rate of the EGR gas flowing through the bypass pipe by the exhaust temperature. For each interval in which the relationship with the divide value is linearly approximated A calculation means is a first-order function was similar,
An exhaust gas recirculation device for an internal combustion engine, comprising:

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