JP4429355B2 - Recirculation exhaust gas flow rate calculation device - Google Patents

Description

  The present invention relates to a recirculation exhaust gas flow rate calculation device.

  The amount of gas filled in the cylinder of each cylinder when the intake valve is opened and then closed, that is, the amount of gas charged in the cylinder, is a linear function of the intake pipe pressure, which is the pressure in the intake pipe downstream of the throttle valve. It is already known that it can be expressed by an equation (see Patent Document 1, especially [0013] to [0019] and FIG. 3B, where the vertical axis Q (P) in FIG. (It seems to be (P)). Then, if this linear function equation is obtained in advance, the cylinder charge gas amount can be calculated easily and accurately by measuring the intake pipe pressure, for example. Alternatively, the intake pipe pressure can be calculated from this linear function equation by obtaining the cylinder charge gas amount.

JP-A-8-334050 JP 2002-180877 A

  By the way, in order to make the air-fuel ratio exactly match the target air-fuel ratio, it is necessary to accurately determine the amount of fresh air that is filled into the cylinder, that is, the amount of fresh air that is filled in the cylinder. It is necessary to easily and accurately obtain the value.

  When exhaust gas recirculation gas is not being supplied, the burned gas that has flowed into the intake pipe from the cylinder at the start of the intake stroke is returned to the cylinder during the intake stroke, and is filled into the cylinder. It may be considered that the gas is only fresh air. Then, the amount of fresh air in the cylinder can be calculated easily and accurately using the above-described linear function equation.

  However, when the exhaust gas recirculation gas is supplied, the mixed gas of fresh air and the exhaust gas recirculation gas is filled in the cylinder. Therefore, the mixed gas filled in the cylinder is obtained from the above linear function equation. The amount of fresh air in the cylinder cannot be known.

  Therefore, an object of the present invention is to easily and accurately obtain the amount of fresh air in the cylinder or the intake pipe pressure when the exhaust gas recirculation gas is being supplied, and therefore perform engine control easily and accurately. An object of the present invention is to provide a control device for an internal combustion engine.

  In order to solve the above problems, according to the present invention, an intake pipe and an exhaust pipe downstream of a throttle valve are connected to each other through an exhaust gas recirculation passage, and exhaust gas in the exhaust pipe is connected to the inside of the intake pipe through an exhaust gas recirculation passage. In the internal combustion engine in which an exhaust gas recirculation control valve for controlling the amount of exhaust gas recirculated in the intake pipe is disposed in the exhaust gas recirculation passage, the exhaust gas recirculation The control valve passage recirculation exhaust gas flow rate that is the flow rate of the recirculation exhaust gas that passes through the control valve is the two linear function equations of the intake pipe pressure that is the pressure in the intake pipe downstream of the throttle valve, and the gradients are different from each other. In addition, a control valve passage recirculation exhaust gas flow rate calculation device for calculating by two linear function formulas continuous at the connection point is provided.

  The recirculation exhaust gas flow rate passing through the control valve can be calculated easily and accurately.

  FIG. 1 shows a case where the present invention is applied to a spark ignition type internal combustion engine. However, the present invention can also be applied to a compression ignition type internal combustion engine.

  Referring to FIG. 1, for example, 1 is an engine body having four cylinders, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an intake valve, 7 is an intake port, and 8 is an exhaust. Reference numeral 9 denotes an exhaust port, 10 denotes a spark plug, and 11 denotes a fuel injection valve. The intake port 7 is connected to a surge tank 13 via a corresponding intake branch pipe 12, and the surge tank 13 is connected to an air cleaner 15 via an intake duct 14. A throttle valve 17 driven by a step motor 16 is disposed in the intake duct 14. In the present specification, the intake duct downstream from the throttle valve 17, the surge tank 13, the intake branch pipe 12, and the intake port 7 may be referred to as an intake pipe.

  On the other hand, the exhaust port 9 is connected to a catalytic converter 20 via an exhaust manifold 18 and an exhaust pipe 19, and this catalytic converter 20 is communicated to the atmosphere via a muffler (not shown).

  The exhaust manifold 18 and each intake branch pipe 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) supply pipe 21, and an electrically controlled EGR control valve 22 is disposed in the EGR supply pipe 21. . In the internal combustion engine shown in FIG. 1, an EGR supply pipe 21 downstream of the EGR control valve 22 is branched and connected to each intake branch pipe 12. The EGR control valve 22 includes a step motor. When the step number STP of the step motor increases, the opening degree of the EGR control valve 22 increases. That is, the step number STP represents the opening degree of the EGR control valve 22.

  The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36. It comprises. A pressure sensor 39 for detecting an intake pipe pressure Pm, which is a pressure in the intake pipe, is attached in the surge tank 13. The throttle valve 17 is provided with a throttle opening sensor 40 for detecting the throttle opening θt. Further, a load sensor 42 for detecting the depression amount of the accelerator pedal 41 is connected to the accelerator pedal 41. The amount of depression of the accelerator pedal 41 represents the required load. The output signals of these sensors 39, 40, and 42 are input to the input port 35 via corresponding AD converters 37, respectively. Further, a crank angle sensor 43 that generates an output pulse every time the crankshaft rotates, for example, 30 ° is connected to the input port 35. The CPU 34 calculates the engine speed NE based on the output pulse of the crank angle sensor 43. On the other hand, the output port 36 is connected to the spark plug 10, the fuel injection valve 11, the step motor 16, and the EGR control valve 22 through corresponding drive circuits 38, which are based on output signals from the electronic control unit 30. Be controlled.

  In the internal combustion engine shown in FIG. 1, the fuel injection amount QF is calculated based on the following equation, for example.

QF = kAF · KL
Here, kAF represents an air-fuel ratio setting coefficient, and KL represents an engine load factor (%).

  The air-fuel ratio setting coefficient kAF is a coefficient representing the target air-fuel ratio, and decreases when the target air-fuel ratio increases, that is, becomes lean, and increases when the target air-fuel ratio decreases, that is, when it becomes rich. This air-fuel ratio setting coefficient kAF is stored in advance in the ROM 32 as a function of the engine operating state, for example, the required load and the engine speed.

  On the other hand, the engine load factor KL represents the amount of fresh air filled in the cylinder of each cylinder, and is defined by the following equation, for example.

Here, Mcair is the in-cylinder charged fresh air amount (g) that is the amount of fresh air that is filled in the cylinder of each cylinder when the intake valve 7 is opened and then closed, and DSP is the engine exhaust. The amount (liter), NCYL indicates the number of cylinders, and ρastd indicates the air density (about 1.2 g / liter) in the standard state (1 atm, 25 ° C.).

  Therefore, in order to make the actual air-fuel ratio exactly coincide with the target air-fuel ratio, the engine load factor KL needs to be obtained accurately.

  When the EGR control valve 22 is opened and therefore EGR gas is supplied, a mixed gas of fresh air and EGR gas is drawn into the cylinder of each cylinder. Therefore, when the intake valve 7 is opened and then closed, the amounts of the mixed gas and EGR gas filled in the cylinders of the respective cylinders are referred to as an in-cylinder charged gas amount Mc and an in-cylinder charged EGR gas amount Mcegr, respectively. Then, the cylinder filling gas amount Mc is expressed as the sum of the cylinder filling fresh air amount Mcair and the cylinder filling EGR gas amount Mcegr (Mc = Mcair + Mcegr).

  By the way, as described at the beginning, it is known that the cylinder charge gas amount Mc is expressed by a linear function expression of the intake pipe pressure Pm when the intake valve 7 is closed. That is, according to theory and empirical rule, the cylinder charge gas amount Mc is proportional to the cylinder pressure when the intake valve 7 is closed, and this cylinder pressure is the mixed gas pressure upstream of the intake valve 7, that is, the intake pipe. It almost corresponds to the pressure Pm.

  When EGR gas is not supplied, considering that burned gas that has flowed into the intake pipe from the cylinder at the start of the intake stroke is returned to the cylinder during the intake stroke, only fresh air is filled into the cylinder. In this case, the in-cylinder charged fresh air amount Mcair and therefore the engine load factor KL can be expressed by a linear function expression of the intake pipe pressure Pm. That is, the engine load factor KL can be obtained easily and accurately.

  However, the situation is completely different when EGR gas is supplied, and not only fresh air but also EGR gas is filled in the cylinder. For this reason, conventionally, it has been considered that the in-cylinder charged fresh air amount Mair or the engine load factor KL cannot be expressed by a linear function expression of the intake pipe pressure Pm.

  If the cylinder filling EGR gas amount Mcegr can be expressed by a linear function expression of the intake pipe pressure Pm, the cylinder filling gas quantity Mc can be expressed by a linear function expression of the intake pipe pressure Pm, and the cylinder filling gas amount. Considering that Mc is the sum of the in-cylinder charged fresh air amount Mcair and the in-cylinder charged EGR gas amount Mcegr, the in-cylinder charged fresh air amount Mcair or the engine load factor KL is expressed by a linear function expression of the intake pipe pressure Pm. be able to.

  However, conventionally, it has been considered that the cylinder filling EGR gas amount Mcegr cannot be expressed by a linear function expression of the intake pipe pressure Pm. This will be described with reference to FIG.

  First, as shown in FIG. 2A, the EGR gas pressure upstream of the EGR control valve 22 is the exhaust pressure Pe (kPa) in the exhaust manifold 18, and the EGR gas temperature upstream of the EGR control valve is in the exhaust manifold 18. EGR control that is the flow rate of EGR gas passing through the EGR control valve 22 is considered that the exhaust gas temperature Te (K) and the pressure of the EGR gas passing through the EGR control valve 22 is the intake pipe pressure Pm (kPa). The valve passage gas flow rate megr (g / sec) can be expressed by the following equation (1).

Here, μ is a flow coefficient in the EGR control valve 22, Ae is an opening cross-sectional area (m ² ) of the EGR control valve 22, Re is a constant related to the gas constant R, and Φ (Pm / Pe) is Pm / Pe. Each function is represented. The flow coefficient μ and the opening cross-sectional area Ae are values determined by the opening degree θe of the EGR control valve 22, and the constant Re is a value obtained by dividing the gas constant R by the mass Me of exhaust gas or EGR gas per mol ( Re = R / Me).

  Further, the function Φ (Pm / Pe) is expressed by the following equation using the specific heat ratio κ (constant) so that the flow rate of the EGR gas does not exceed the speed of sound.

  The above-described equation (1) will be briefly described. The conservation laws of mass, energy, and momentum for the EGR gas upstream and downstream of the EGR control valve 22 and the state of the EGR gas upstream and downstream of the EGR control valve 22 are described. Derived using equations.

  Here, if the exhaust pressure Pe is the atmospheric pressure Pa in order to simplify the calculation, the EGR control valve passage gas flow rate megr represented by the equation (1) is as shown in FIG. That is, the EGR control valve passage gas flow rate megr is maintained substantially constant when the intake pipe pressure Pm is small, and when the intake pipe pressure Pm becomes high, non-linearity with respect to the intake pipe pressure Pm as indicated by NR in FIG. Decreases toward the atmospheric pressure Pa. The nonlinear part NR is due to the part of Pe / √Te and the function Φ (Pm / Pe) in the equation (1).

  Therefore, it was considered that the EGR control valve passage gas flow rate megr, in particular, the nonlinear portion NR cannot be expressed by a linear function expression of the intake pipe pressure Pm. However, if a considerably large number of linear function equations are used, it is considered that the EGR control valve passage gas flow rate megr can be expressed by a linear function equation of the intake pipe pressure Pm. However, in this case, the engine load factor KL can no longer be simply obtained.

  However, according to the inventors of the present application, the EGR control valve passage gas flow rate megr can be expressed by two linear function expressions of the intake pipe pressure Pm. Accordingly, the in-cylinder charged fresh air amount Mcair or the engine load factor KL can be expressed by the intake pipe. It was found that it can be expressed by two linear function expressions of the pressure Pm.

  That is, first, as shown in FIG. 3, the exhaust temperature Te increases significantly with respect to the increase in the intake pipe pressure Pm than the exhaust pressure Pe increases, and as a result, Pe / √Te is set to the intake pipe pressure Pm. It can be expressed by a linear function expression.

  The function Φ (Pm / Pe) can also be expressed by a linear function expression of the intake pipe pressure Pm. This will be described with reference to FIG. Considering that the exhaust pressure Pe is not maintained at a constant atmospheric pressure Pa but varies according to the intake pipe pressure Pm, as shown in FIG. 4A, when the intake pipe pressure Pm is Pm1, The function Φ (Pm / Pe) is not on the curve Ca that converges to the atmospheric pressure Pa, but on the curve C1 that converges to the exhaust pressure Pe1, and this is represented by a plot (◯). Similarly, Φ (Pm / Pe) when Pm = Pm2 (> Pm1) is on the curve C2 that converges to the exhaust pressure Pe2 (> Pe1), and Φ (Pm / Pm / Pm3) when Pm = Pm3 (> Pm2). Pe) is on the curve C3 that converges to the exhaust pressure Pe3 (> Pe2).

  The plot obtained in this way can be connected by a straight line L2, as shown in FIG. Therefore, the function Φ (Pm / Pe) is a linear function expression of the intake pipe pressure Pm corresponding to the straight line L1 when the intake pipe pressure Pm is small, and the primary function of the intake pipe pressure Pm corresponding to the straight line L2 when the intake pipe pressure Pm is large. Therefore, it can be expressed by two linear function expressions of the intake pipe pressure Pm. That is, the EGR control valve passage gas flow rate megr can be expressed by two linear function expressions of the intake pipe pressure Pm.

  Here, during steady operation, an EGR control valve passage gas flow rate megr that is the amount of EGR gas flowing into the intake pipe per unit time, and the amount of EGR gas that flows out of the intake pipe and flows into the cylinder per unit time. A certain in-cylinder intake EGR gas amount mcegr (g / sec) is equal to each other. The in-cylinder charged EGR gas amount Mcegr is obtained by multiplying the in-cylinder intake EGR gas amount mcegr by the time ΔT (sec) required for one intake stroke of each cylinder (Mcegr = mcegr · ΔT). .

  Then, the in-cylinder charged EGR gas amount Mcegr at the time of steady operation can be expressed by a linear function expression of the intake pipe pressure Pm.

  Therefore, the in-cylinder charged fresh air amount Mair or the engine load factor KL at the time of steady operation can be expressed by two linear function expressions of the intake pipe pressure Pm. This is the basic idea of the present invention.

  FIG. 5 shows an example of two linear function expressions of the intake pipe pressure Pm representing the engine load factor KL during steady operation when the engine speed NE and the EGR control valve opening STP are constant. Yes. As shown in FIG. 5, the engine load factor KL is expressed by two linear function expressions of the intake pipe pressure Pm having different gradients and continuous at the connection point CP. That is, the engine load factor KL is expressed by a linear function expression of the gradient a1 when the intake pipe pressure Pm is small, and by a linear function expression of the gradient a2 when the intake pipe pressure Pm is high.

  Here, if the gradients of the two linear function equations are a1 and a2, respectively, and the intake pipe pressure and the engine load factor at the connection point CP are b and c, respectively, these two linear function equations can be expressed by the following equations. .

KL = a1 · (Pm−b) + c... Pm ≦ b
KL = a2 · (Pm−b) + c... Pm> b
These are collectively expressed as the following formula (2).

KL = a · (Pm−b) + c (2)
a = a1 Pm ≦ b
a = a2 Pm> b
In the embodiment according to the present invention, two linear function expressions of the intake pipe pressure Pm representing the engine load factor KL during steady operation are stored in advance in the ROM 32 in the form shown in the expression (2). In this way, two linear function expressions can be represented by three parameters a, b, and c. That is, it is possible to reduce the number of parameters necessary for expressing the two linear function expressions.

  In the embodiment according to the present invention, in consideration of the fact that the opening sectional area Ae of the EGR control valve 22 in the above equation (1) depends on the EGR control valve opening STP and the engine charging efficiency depends on the engine speed NE. The parameters a (a1, a2), b, and c are set according to the EGR control valve opening STP or the engine speed NE.

  Specifically, as shown in FIG. 6A, the gradient a1 increases as the engine speed NE increases when the engine speed NE is low, and the engine speed NE increases when the engine speed NE is high. It becomes smaller as it becomes higher, and further becomes larger as the EGR control valve opening STP becomes larger. Further, as shown in FIG. 6B, the gradient a2 increases as the engine speed NE increases when the engine speed NE is low, and decreases as the engine speed NE increases when the engine speed NE is high. Furthermore, it becomes larger as the EGR control valve opening STP becomes larger. These gradients a1 and a2 are obtained in advance by experiments, and stored in advance in the ROM 32 in the form of maps shown in FIGS. 6C and 6D as functions of the engine speed NE and the EGR control valve opening STP, respectively. Has been.

  On the other hand, the intake pipe pressure b at the connection point CP decreases as the engine speed NE increases as shown in FIG. The intake pipe pressure b at the connection point CP is also obtained in advance by experiments and is stored in advance in the ROM 32 in the form of a map shown in FIG. 7 as a function of the engine speed NE.

  Further, as shown in FIG. 8A, the engine load factor c at the connection point CP increases as the engine rotational speed NE increases when the engine rotational speed NE is low, and the engine rotational speed when the engine rotational speed NE is high. It becomes smaller as NE becomes higher, and further becomes smaller as EGR control valve opening STP becomes larger. The engine load factor c at the connection point CP is also obtained in advance by experiments, and is stored in advance in the ROM 32 as a function of the engine speed NE and the EGR control valve opening STP in the form of a map shown in FIG. Yes.

  Therefore, generally speaking, for each of a plurality of EGR control valve openings STP different from each other, two linear function expressions of the intake pipe pressure Pm representing the in-cylinder charged fresh air amount Mair or the engine load factor KL are obtained in advance. Will be remembered. In addition, two linear function equations of the intake pipe pressure Pm representing the in-cylinder charged fresh air amount Mair or the engine load factor KL are obtained and stored in advance for a plurality of different engine speeds NE. Become.

  FIG. 9 shows an example of two linear function expressions of the intake pipe pressure Pm representing the engine load factor KL during steady operation at a constant engine speed NE and various EGR control valve opening STP. The broken line in FIG. 9 indicates the engine load factor KL when EGR gas is not supplied, that is, when the EGR control valve opening STP is zero.

  Therefore, if the intake pipe pressure Pm is detected by, for example, the pressure sensor 39, the engine load factor KL can be accurately and easily obtained from the detected intake pipe pressure Pm using the above-described equation (2). Thus, the air-fuel ratio can be accurately and easily matched with the target air-fuel ratio.

  The fact that the engine load factor KL can be expressed by a linear function expression of the intake pipe pressure Pm in this way means that it is not necessary to create a map that represents the relationship between the engine load factor KL and the intake pipe pressure Pm. Therefore, the map creation effort is eliminated first. It also means that it is not necessary to solve complicated differential equations, for example, and therefore the calculation load on the CPU 34 is reduced.

  FIG. 10 shows a routine for calculating the fuel injection amount QF in the above-described embodiment according to the present invention. This routine is executed by interruption every predetermined crank angle.

  Referring to FIG. 10, first, at step 100, the intake pipe pressure Pm, the engine speed NE, and the EGR control valve opening STP are read. In the subsequent step 101, the intake pipe pressure b and the engine load factor c at the connection point CP are calculated from the maps of FIGS. 7 and 8B. In the following step 102, it is determined whether or not the detected intake pipe pressure Pm is equal to or lower than the intake pipe pressure b at the connection point. When Pm ≦ b, the routine proceeds to step 103 where a1 is calculated from the map of FIG. In the subsequent step 104, the gradient a is set to a1. Next, the routine proceeds to step 107. On the other hand, when Pm> b, the routine proceeds to step 105, where a2 is calculated from the map of FIG. In the subsequent step 106, the gradient a is set to a2. Next, the routine proceeds to step 107.

  In step 107, the engine load factor KL is calculated based on the equation (2) (KL = a · (Pm−b) + c). In the subsequent step 108, the air-fuel ratio setting coefficient kAF is calculated based on the engine operating state, and in the subsequent step 109, the fuel injection amount QF is calculated (QF = kAF · KL). Fuel is injected from each fuel injection valve 11 by QF.

  Therefore, generally speaking, the intake pipe pressure Pm is obtained, the in-cylinder charged fresh air amount Mcair or the engine load factor KL is calculated from the intake pipe pressure Pm using the linear function equation (2), and the calculated in-cylinder It means that the engine operation is controlled based on the charged fresh air amount Mcair or the engine load factor KL.

  In the embodiments according to the present invention described so far, the engine load factor KL is calculated from the intake pipe pressure Pm detected by the pressure sensor 39. However, for example, the intake pipe pressure Pm is estimated based on the throttle opening or the output of an air flow meter arranged in the intake duct 14 upstream of the throttle valve 17, and the engine load factor KL is calculated from the estimated intake pipe pressure Pm. You can also Alternatively, for example, the intake pipe pressure Pm may be estimated using a calculation model, and the engine load factor KL may be calculated from the estimated intake pipe pressure Pm.

  By the way, when the above-described linear function expression (2) of the intake pipe pressure Pm is rewritten into a linear function expression of the engine load factor KL representing the intake pipe pressure Pm, the following expression (3) is obtained.

Pm = (1 / a). (KL-c) + b (3)
a = a1 KL ≦ c
a = a2 KL> c
Therefore, the intake pipe pressure Pm can be calculated using the equation (3) from the engine load factor KL or the in-cylinder charged fresh air amount.

1 is an overall view of an internal combustion engine. It is a figure for demonstrating EGR control valve passage gas amount megr. FIG. 3 is a diagram showing exhaust pressure Pe, exhaust temperature Te, and Pe / √Te. It is a diagram showing a function Φ (Pm / Pe). It is a diagram which shows an example of the relationship between the engine load factor KL and the intake pipe pressure Pm. It is a diagram which shows gradient a1, a2. It is a diagram which shows the intake pipe pressure b in a connection point. It is a diagram which shows the engine load factor c in a connection point. It is a diagram which shows an example of the relationship between the engine load factor KL and the intake pipe pressure Pm. It is a flowchart which shows the calculation routine of the fuel injection quantity QF.

Explanation of symbols

1 Engine Body 12 Intake Branch Pipe 17 Throttle Valve 18 Exhaust Manifold 21 EGR Supply Pipe 22 EGR Control Valve

Claims (1)

  The intake pipe and exhaust pipe downstream of the throttle valve are connected to each other through an exhaust gas recirculation passage so that the exhaust gas in the exhaust pipe is recirculated into the intake pipe through the exhaust gas recirculation passage, and is recirculated into the intake pipe. This is the flow rate of the recirculated exhaust gas that passes through the exhaust gas recirculation control valve in an internal combustion engine in which an exhaust gas recirculation control valve for controlling the amount of exhaust gas to be discharged is disposed in the exhaust gas recirculation passage. The control valve passage recirculation exhaust gas flow rate is two linear function expressions of the intake pipe pressure which is the pressure in the intake pipe downstream of the throttle valve, and the gradient functions are different from each other and are continuous at the connection point. Control valve passage recirculation exhaust gas flow rate calculation device which calculates by

Images