JP5480048B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine that includes an exhaust gas recirculation (EGR) pipe that connects an exhaust passage of the internal combustion engine and an intake pipe.

Conventionally, for example, Patent Document 1 discloses a method for estimating a flow rate of intake gas sucked into a cylinder using an intake valve model in relation to fuel injection amount control in an internal combustion engine. The intake gas amount is determined when the intake valve is closed, and is proportional to the in-cylinder pressure at that time. The in-cylinder pressure when the intake valve is closed can be regarded as equal to the pressure upstream of the intake valve, that is, the intake pipe pressure. Therefore, it can be said that the amount of intake gas is proportional to the intake pipe pressure. Under such a premise, the intake valve model of Patent Document 1 obtains an intake gas flow rate mc ^** sucked into the cylinder according to the following formula (1) based on an empirical rule, and uses the intake gas flow rate mc ^** . Thus, the amount of intake gas sucked into the cylinder in one intake stroke is obtained.
_{^{mc ** = (T 0 / Tm}} **) · (c · Pm ** -d) ··· (1)
In the above formula (1), ^{Pm **} is the intake pipe pressure, _{T 0} is the intake air temperature (atmospheric temperature), ^{Tm **} is the intake pipe gas temperature. Further, c is a proportional coefficient, and d is a value representing burned gas remaining in the cylinder.

A specific method for estimating the intake gas flow rate mc ^** is as follows. That is, this intake valve model stores tables that define the relationship between the engine speed Ne, the intake valve opening / closing timing VT, the maximum lift amount Lmax of the intake valve, the proportional coefficient c, and the burned gas amount d. The proportional coefficient c and the burned gas amount d are obtained from the actual engine speed Ne, the intake valve opening / closing timing VT, the intake valve maximum lift amount Lmax, and the respective tables. This intake valve model applies the separately estimated intake pipe pressure Pm ^** and intake pipe gas temperature Tm ^** to the above equation (1) when determining the proportionality coefficient c and burned gas amount d. The intake gas flow rate mc ^** is estimated.

International Publication No. 03/033897

By the way, it is assumed that the intake valve model is applied to an internal combustion engine having an EGR pipe. As a result, exhaust gas (external EGR gas) flowing through the EGR pipe flows into the intake pipe, so that the amount of gas in the intake pipe changes abruptly. That is, since the value of the burned gas amount d in the above equation (1) changes, the estimation accuracy of the intake gas flow rate mc ^** decreases. Therefore, if the intake valve model is applied as it is, the estimation accuracy of the intake gas flow rate is reduced. In order to prevent such a decrease in estimation accuracy, the burned gas amount d may be obtained again. However, if the burnt gas amount d is obtained again, the calculation time is extended, and there is a problem that the controllability deteriorates.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a control device for an internal combustion engine that can estimate the intake gas flow rate with high accuracy even when using EGR.

In order to achieve the above object, a first invention is an intake valve model for calculating a flow rate of intake gas sucked into a cylinder by using at least a gas temperature and an intake pipe pressure in an intake pipe of an internal combustion engine. An internal combustion engine control device comprising:
An atmospheric temperature acquisition means for acquiring the atmospheric temperature;
An EGR pipe connecting the exhaust passage of the internal combustion engine and the intake pipe;
Recirculation exhaust gas flow rate acquisition means for acquiring a recirculation exhaust gas flow rate flowing through the EGR pipe;
Recirculation exhaust gas temperature acquisition means for acquiring a recirculation exhaust gas temperature flowing through the EGR pipe;
Applying the intake gas flow rate, the atmospheric temperature, and the recirculated exhaust gas flow rate to the model related to the gas in the intake pipe upstream from the connection with the EGR pipe, the gas temperature in the upstream intake pipe is increased upstream. Upstream gas temperature estimating means for estimating the gas temperature;
Downstream intake pipe pressure acquisition means for acquiring, as a downstream intake pipe pressure, an intake pipe pressure in an intake pipe downstream of a connection portion with the EGR pipe;
Wall surface temperature acquisition means for acquiring the wall surface temperature of the downstream intake pipe;
Applying the atmospheric temperature, the recirculated exhaust gas flow rate, the recirculated exhaust gas temperature, the downstream intake pipe pressure and the wall surface temperature to the model related to the gas in the downstream intake pipe, the gas in the downstream intake pipe Downstream gas temperature estimating means for estimating temperature as downstream gas temperature;
An intake gas flow rate calculating means for calculating an intake gas flow rate to be sucked into a cylinder by applying the upstream gas temperature, the downstream intake pipe pressure and the downstream gas temperature to the intake valve model;
It is characterized by providing.

The second invention is the first invention, wherein
An EGR cooler provided in the EGR pipe;
The recirculation exhaust gas temperature acquisition means acquires the temperature of the EGR cooler as the recirculation exhaust gas temperature.

  According to the first invention, the gas temperature (upstream gas temperature) in the intake pipe upstream from the connection portion with the EGR pipe and the gas temperature (downstream gas temperature) in the intake pipe downstream are estimated and acquired. Together with the downstream intake pipe pressure, these can be applied to the intake valve model to calculate the intake gas flow rate. When the exhaust gas is recirculated into the intake pipe, the gas density in the intake pipe changes. Here, the gas density in the intake pipe is inversely proportional to the gas temperature in the intake pipe. Therefore, if the upstream gas temperature and the downstream gas temperature are estimated and applied to the intake valve model, it is possible to correct the gas density change in the intake pipe. Therefore, even when EGR is used, the intake gas flow rate can be estimated with high accuracy.

  According to the second aspect of the invention, the recirculated exhaust gas temperature necessary for estimating the downstream gas temperature can be substituted by the EGR cooler temperature. Therefore, an increase in the system can be prevented.

It is a figure for demonstrating the system configuration | structure of embodiment. It is the functional block diagram which showed the connection relation of the model used when the control apparatus of embodiment estimates the amount of intake gas. It is the figure which showed an example of the suction gas flow rate correction coefficient α (= Tm ^{* i} / Tm ⁱ ). It is a figure showing change of the amount of inhalation gas with respect to an EGR rate. ECU70 is a flowchart showing a calculation procedure of the intake pipe gas temperature Tm ⁱ performed by the. 4 is a flowchart showing a procedure for calculating an intake pipe gas temperature Tm ^{* i} executed by an ECU 70; 3 is a flowchart showing a procedure for calculating an intake gas flow rate mc ⁱ executed by an ECU 70. It is a figure for demonstrating the modification of embodiment. It is a figure for demonstrating the modification of embodiment. It is a figure for demonstrating the modification of embodiment.

[Description of system configuration]
Hereinafter, embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a diagram for explaining a system configuration according to an embodiment of the present invention. The system of this embodiment includes an engine 10 as an internal combustion engine. The number of cylinders and the cylinder arrangement of the engine 10 are not particularly limited.

  The engine 10 includes a cylinder block 14 having a piston 12 therein. The piston 12 is connected to the crankshaft 16 via a crank mechanism. A crank angle sensor 18 is provided in the vicinity of the crankshaft 16. The crank angle sensor 18 is configured to detect the rotation angle (crank angle) of the crankshaft 16.

  A cylinder head 20 is assembled to the upper part of the cylinder block 14. A space from the upper surface of the piston 12 to the cylinder head 20 forms a combustion chamber 22. The cylinder head 20 is provided with a spark plug 24 that ignites the air-fuel mixture in the combustion chamber 22. The cylinder head 20 includes an intake port 26 that communicates with the combustion chamber 22. An intake valve 28 is provided at a connection portion between the intake port 26 and the combustion chamber 22. The intake valve 28 is connected to the variable valve mechanism 30. The variable valve mechanism 30 is configured to change the valve opening characteristics (open / close valve timing, operating angle, lift amount) of the intake valve 28.

  The intake port 26 is provided with an injector 32 that injects fuel near the intake port 26. An intake pipe 34 is connected to the intake port 26. The intake pipe 34 is provided with an air cleaner 36, a throttle valve 38, and a surge tank 40 in order from the upstream side. The throttle valve 38 is constituted by an electronically controlled butterfly valve that opens and closes between a fully closed position and a fully open position, and is driven based on the accelerator opening detected by the accelerator opening sensor 42. The surge tank 40 forms a space having a certain extent in the middle of the intake pipe 34 in order to exhibit an attenuation effect of intake pulsation and the like.

  Further, an exhaust pipe 44 communicating with the combustion chamber 22 is connected to the cylinder head 20. One end of an EGR pipe 46 is connected to the exhaust pipe 44. The other end of the EGR pipe 46 is connected to the surge tank 40. An EGR cooler 48 is provided in the middle of the EGR pipe 46. The EGR cooler 48 is configured to cool the exhaust gas flowing through the EGR pipe 46. An EGR valve 50 is provided in the EGR pipe 46 closer to the intake pipe 34 than the EGR cooler 48. The EGR valve 50 is, for example, a flow control valve that is opened and closed by a stepping motor. When the EGR valve 50 is opened, a part of the exhaust gas flowing through the exhaust pipe 44 is circulated to the intake pipe 34 through the EGR pipe 46 and the EGR cooler 48.

  Further, the system of the present embodiment includes an ECU (Electronic Control Unit) 60. On the input side of the ECU 70, in addition to the crank angle sensor 18 and the accelerator opening sensor 42 described above, the atmospheric temperature detection means 52, the atmospheric pressure detection means 54, the intake pipe pressure detection means 56, the wall surface temperature detection means 58, the reflux exhaust gas The flow rate detection means 60, the recirculation exhaust gas temperature detection means 62, and other various sensors necessary for controlling the vehicle and the engine 10 are connected.

Here, the atmospheric temperature detection means 52, the upstream temperature of the throttle valve 38 (i.e., atmospheric temperature) is used to detect the T _O, atmospheric pressure detecting means 54, the upstream pressure of the throttle valve 38 (i.e., large Atmospheric pressure) for detecting _PO . The intake pipe pressure detecting means 56 is for detecting the intake pipe pressure Pm in the intake pipe 34 downstream of the connecting portion with the EGR pipe 46, and the wall surface temperature detecting means 58 is connected to the EGR pipe 46. than the connecting portion is for detecting the wall temperature T _w of the intake pipe 34 on the downstream side. The recirculation exhaust gas flow rate detection means 60 is for detecting the recirculation exhaust gas flow rate m _EGR flowing through the EGR pipe 46 and flowing into the intake pipe 34, and the recirculation exhaust gas temperature detection means 62 is the EGR pipe 46. _Is for detecting the recirculated exhaust gas temperature T _EGR flowing through the intake pipe 34 and flowing into the intake pipe 34.

  On the other hand, various actuators including an ignition plug 24, an injector 32, a throttle valve 38, and the like are connected to the output side of the ECU 70. The ECU 70 controls the operation of the engine 10 by detecting the operation information of the engine 10 using the various sensors described above and driving each actuator based on the detection result.

[Fuel injection amount control]
One of the operation controls of the engine 10 by the ECU 70 is fuel injection amount control. This fuel injection amount control predicts an intake gas amount Mc that will be sucked into the combustion chamber 22 when the intake valve 28 is closed before the intake valve closes, and is based on the following equation (2). The fuel injection amount fc is determined. fc = K · Mc (2)
In the above equation (2), K is a coefficient that changes according to the target air-fuel ratio.

  FIG. 2 is a functional block diagram showing a connection relationship of models used when the ECU 70 predicts the intake gas amount Mc. When the system of the present embodiment estimates the intake gas amount Mc, as shown in FIG. 2, an electronically controlled throttle model M10, a throttle model M20, an upstream intake pipe model M30, a downstream intake pipe model M40, and an intake valve model M50 are used. Use the simulation model.

(Electronic control throttle model M10)
Electronic control throttle model M10, based on the accelerator pedal operation amount AA to date, is a model for estimating the throttle valve opening θt of the predetermined time T _A destination time t from the current time. In the present embodiment, the electronically controlled throttle model M10 has an accelerator pedal detected by the accelerator opening sensor 42 in a table that defines the relationship between the accelerator pedal operation amount AA and the target throttle valve opening θr separately stored in the ECU 70. A provisional target throttle valve opening θr1 is obtained by applying the operation amount AA. A value obtained by delaying the provisional target throttle valve opening θr1 by a predetermined time T is determined as the final target throttle valve opening θr.

As described above, the target throttle valve opening θr is equal to the temporary target throttle valve opening θr1 determined according to the accelerator pedal operation amount AA at the time before the predetermined time T from the current time. T _a only the aforementioned time t target throttle opening θr in is equal to the provisional target throttle valve opening θr1 before time from the present time (T-T _a). Further, the provisional target throttle valve opening θr1 before the time (T−T _A ) from the present time is equal to the throttle valve opening θt if the operation delay time of the throttle valve is ignored. Based on this idea, the electronically controlled throttle model M10 estimates the throttle valve opening θt at time t that is a predetermined time T _A ahead of the current time. That is, the provisional target throttle valve opening θr1 before the time (T−T _A ) from the current time is estimated as the throttle valve opening θt at the time t that is a predetermined time T _A from the current time.

(Throttle model M20)
The throttle model M20 was obtained based on physical laws such as energy conservation law, momentum conservation law, mass conservation law, and state equation such as the flow rate of fresh air passing through the throttle valve 38 (throttle passage fresh air flow rate) mt. It is a model estimated based on following formula (3) and following formula (4). Throttle model M20, the upstream pressure P ₀ of the throttle valve 38 is, the pressure on the downstream side, specifically, from the installation of the throttle valve 38, an intake pipe 34 to the connecting portion between the EGR pipe 46 (hereinafter, simply In the case of a forward flow larger than the intake pipe pressure Pm ^* in “the upstream intake pipe section”), the following equation (3) is used, and when the throttle valve upstream pressure P ₀ is a reverse flow smaller than the intake pipe pressure Pm ^*. The following formula (4) is used. As a result, the throttle fresh air flow rate mt has a positive value in the case of forward flow, and a negative value in the case of reverse flow.

In the above formulas (3) and (4), T ₀ is the upstream temperature of the throttle valve 38, Tm ^* is the upstream intake pipe section intake pipe gas temperature, R is the gas constant, and κ is the specific heat ratio (physical property value). Represent each. In the above equations (3) and (4), θt is the throttle valve opening estimated by the electronically controlled throttle model M10, Ct (θt) is a flow coefficient that changes according to the throttle valve opening θt, At ( θt) represents the throttle opening area (opening area of the intake pipe 34) that changes according to the throttle valve opening θt. For the flow coefficient Ct (θt), the throttle model M20 applies the estimated throttle valve opening θt to a table that defines the relationship between the throttle valve opening θt and the flow coefficient Ct (θt) separately stored in the ECU 70. It is required by that. Similarly, At (θt) is obtained by applying the estimated throttle valve opening θt to the table in which the throttle model M20 defines the relationship between the throttle valve opening θt and the opening area At (θt).

Specifically, the throttle model M20 acquires the upstream pressure P _{0 of} the throttle valve 38 and the upstream temperature T ₀ of the throttle valve 38 from the atmospheric pressure detection means 54 and the atmospheric temperature detection means 52, respectively, and the intake pipe pressure Pm ^*. Is obtained from an upstream intake pipe model M30, which will be described later, and these values are applied to the above equation (3) or (4) to estimate the throttle passage fresh air flow rate mt at time t.

Here, the derivation process of the above equations (3) and (4) describing the throttle model M20 will be described. The opening cross-sectional area upstream of the throttle valve 38 is Au, the fresh air density is ρu, the fresh air flow velocity is vu, the opening cross-sectional area of the intake pipe 34 by the throttle valve 38 is Ad, the fresh air density is ρd, and the throttle If the flow velocity of fresh air passing through the valve 38 is vd, the fresh air flow rate mt passing through the throttle can be expressed by the following equation (5). The following formula (5) can be said to be a formula describing the law of conservation of mass.
mt = Ad · ρd · vd = Au · ρu · vu (5)

On the other hand, the kinetic energy, when the mass of fresh air and _{m AIR,} a _m AIR · ^vu 2/2 upstream of the throttle valve 38, a _m AIR · ^vd 2/2 at a location passing through the throttle valve 38. On the other hand, the thermal energy is m _AIR · Cp · Tu upstream of the throttle valve 38 and m _AIR · Cp · Td where it passes through the throttle valve 38. Therefore, the following formula (6) is obtained according to the energy conservation law. Note that Tu is the fresh air temperature upstream of the throttle valve, Td is the fresh air temperature downstream of the throttle valve, and Cp is the constant pressure specific heat.
^{_{m AIR · vu 2/2 +}} m AIR · Cp · Tu = m AIR · vd 2/2 + m AIR · Cp · Td ··· (6)

By the way, the equation of state can be expressed by the following equation (7), the specific heat ratio κ can be expressed by the following equation (8), and the Meyer relationship can be expressed by the following equation (9). T is represented as the following formula (10). P is the gas pressure, ρ is the gas density, T is the gas temperature, R is the gas constant, and Cv is the constant volume specific heat.
P = ρ · R · T (7)
κ = Cp / Cv (8)
Cp = Cv + R (9)
Cp · T = {κ / (κ−1)} · (P / ρ) (10)

When the above equation (6) is rewritten using the relationship of the above equation (10), the following equation (11) is obtained. Note that Pu is the pressure of fresh air upstream of the throttle valve 38, and Pd is the pressure of fresh air at a location passing through the throttle valve 38.
^{_{m AIR · vu 2/2 +}} {κ / (κ-1)} · (Pu / ρu) = m AIR · vd 2/2 + {κ / (κ-1)} · (Pd / ρd) ··· (11 )

Then, considering infinite upstream of the throttle valve 38, Au = ∞ and vu = 0. Therefore, the above equation (11) can be rewritten as the following equation (12).
{Κ / (κ-1) } · (Pu / ρu) = m AIR · vd 2/2 + {κ / (κ-1)} · (Pd / ρd) ··· (12)

Next, the momentum will be described. When the average pressure in the fixed space connecting the portion of the cross-sectional area Au and the portion of the cross-sectional area Ad is Pmean, the following formula (13) is obtained.
ρd · vd ² · Ad−ρu · vu ² · Au = Pu · Au−Pd · Ad + Pmean · (Ad−Au) (13)

When Au = ∞ and vu = 0 in the above formula (13), the following formula (14) is obtained. From the above formula (13) and the following formula (14), the relationship regarding the momentum of the following formula (15) (Relationship based on the law of conservation of momentum) is obtained.
Pmean = Pu (14)
ρd · vd ² = Pu−Pd (15)

  Therefore, the following equation (16) is obtained from the above equations (5), (12), and (15).

In the above equation (16), Pu is the upstream pressure P ₀ of the throttle valve 38 and Pd is the intake pipe pressure Pm ^*. Therefore, Ct (θt) is introduced into the flow coefficient, and the opening cross-sectional area Ad is defined as the opening area At. If rearranged with (θt), the above formula (3) is obtained. Since the derivation process of the above equation (4) is the same as that of the above equation (3), it will be omitted.

(Upstream intake pipe model M30)
The upstream intake pipe model M30 includes the following formulas (17) and (18) based on the law of conservation of mass and the law of conservation of energy, the fresh air flow rate mt passing through the throttle, the intake air temperature T ₀ , the intake gas flow rate mc, and the recirculated exhaust gas. This is a model for obtaining the intake pipe pressure Pm ^* and the intake pipe gas temperature Tm ^* from the flow rate m _EGR . In the following formulas (17) and (18), Vm ^* is the volume of the upstream side intake pipe portion.

d (Pm ^* / Tm ^* ) / dt = (R / Vm ^* ) · {mt− (mc−m _EGR )} (17)
dPm ^* / dt = κ · (R / Vm ^* ) · {mt · T ₀ − (mc−m _EGR ) · Tm ^* } (18)

Specifically, the upstream intake pipe model M30 acquires the upstream temperature T ₀ of the throttle valve 38 and the recirculated exhaust gas flow rate m _EGR from the atmospheric temperature detecting means 52 and the recirculated exhaust gas flow rate detecting means 60, respectively. In addition, the throttle passage fresh air flow rate mt is acquired from the throttle model M20, and the intake gas flow rate mc is acquired from an intake valve model M40 described later. These values are applied to the above equations (17) and (18) to determine the intake pipe pressure Pm ^* and the intake pipe gas temperature Tm ^* at time t.

Here, the derivation process of the above equations (17) and (18) describing the upstream intake pipe model M30 will be described. When the total fresh air amount in the upstream intake pipe portion is M, the temporal change in the total fresh air amount M is the throttle passage fresh air flow rate mt corresponding to the flow rate of fresh air flowing into the upstream intake pipe portion, and the intake air This can be expressed as a difference from the amount of fresh air flowing out from the pipe 34. The amount of fresh air flowing out from the intake pipe 34 is the amount of gas (mc−m _EGR ) obtained by removing the recirculated exhaust gas flow rate m _EGR flowing into the intake pipe 34 from the intake gas flow rate mc sucked into the combustion chamber 22. be equivalent to. From these, the following formula (19) based on the law of conservation of mass is obtained.
dM / dt = mt− (mc−m _EGR ) (19)

Since the state equation can be expressed by the following equation (20), the above equation (17) based on the law of conservation of mass is obtained by eliminating the total fresh air amount M from the above equation (19) and the following equation (20). It is done.
Pm ^* / Vm ^* = M / R / Tm ^* (20)

Next, when the energy conservation law regarding the upstream side intake pipe part is examined, in this case, the volume Vm ^* of the intake pipe part does not change, and most of the energy contributes to the temperature rise (kinetic energy can be ignored). it is conceivable that. Accordingly, the amount of time change of the fresh air energy M · Cv · Tm ^{* in} the upstream intake pipe portion is determined from the fresh air energy Cp · mt · T ₀ flowing into the upstream intake pipe portion and the upstream intake pipe portion. Since it is equal to the difference between the outflowing fresh energy Cp · (mc−m _EGR ) · Tm ^* , the following equation (21) is obtained.
d (M · Cv · Tm ^* ) / dt = Cp · mt · T ₀ −Cp · (mc−m _EGR ) · Tm ^* (21)
The above formula (18) is obtained by transforming the above formula (21) using the above formula (8) and the above formula (20).

(Downstream intake pipe model M40)
The downstream intake pipe model M40 has an intake pipe gas temperature Tm in an intake pipe 34 (hereinafter simply referred to as “downstream intake pipe portion”) from a connection portion with the EGR pipe 46 to a connection portion with the combustion chamber 22. It is a model estimated based on following formula (22) and formula (23). In Formula (22) or formula (23), i, i-1 represents the number of computation steps, Cpa is the specific heat at constant pressure in the upstream side intake pipe portion, Ma ⁱ in fresh air amount on the upstream side intake pipe portion is there. Cp _EGR is a constant pressure specific heat in the downstream side intake pipe part, and M _EGR ⁱ is a recirculated exhaust gas amount in the downstream side intake pipe part. Q is the amount of heat transferred to the suction gas.
Tm ⁱ = Tm ^i-1 + ΔTm ⁱ (22)
ΔTm ⁱ = Q / (Cpa · Ma ⁱ + Cp _EGR · M _EGR ⁱ ) (23)

  When exhaust gas is recirculated into the intake pipe 34, the gas density ρm in the intake pipe 34 changes. The gas density ρm is expressed by ρm = MPm / RTm (M: molecular weight of gas), and is in an inversely proportional relationship with the gas temperature Tm in the intake pipe 34. Therefore, when the flow rate of the recirculated exhaust gas is small, the gas temperature in the intake pipe 34 is low and the gas density in the intake pipe 34 increases, so the amount of intake gas increases. On the other hand, when the flow rate of the recirculated exhaust gas is large, the gas temperature in the intake pipe 34 is high, and the gas density in the intake pipe 34 decreases, so the amount of intake gas decreases. Therefore, by correcting the amount of intake gas by the change in gas density in the intake pipe 34, the amount of intake gas when using the external EGR can be accurately predicted.

  However, since the gas temperature in the downstream side intake pipe section changes abruptly depending on the fresh air flow rate or the recirculated exhaust gas flow rate, it is difficult to detect with high response. Therefore, in the present embodiment, the gas temperature Tm in the downstream side intake pipe portion is estimated based on the above equations (22) and (23).

Here, the derivation process of the above equations (22) and (23) describing the throttle model M40 will be described. The relationship between the heat balance in the downstream side intake pipe part is as follows: heat transfer amount Q to intake gas, heat quantity Q _{EGR of} exhaust gas, heat quantity Qa of fresh air, heat quantity Qc of intake gas sucked into the cylinder, downstream side intake pipe part The amount of heat transfer from the wall surface Qw can be expressed as in the following formula (24).
Q = Q _EGR + Qa-Qc + Qw (24)

Each term on the right side of the above equation (24) can be expressed by the following equations (25) to (28), where Δt is the calculation step time.
Q _EGR = Cp _EGR · m _EGR · T _EGR · Δt (25)
Qa = Cpa · ma · T ₀ · Δt (26)
Qc = Cpa · mc ⁱ⁻¹ · (1−F _EGR ⁱ ) · Tm ⁱ⁻¹ + Cp _EGR · mc ⁱ⁻¹ · F _EGR ⁱ · Tm ⁱ⁻¹ · Δt (27)
Qw = hw · A · (Tw−Tm ⁱ⁻¹ ) · Δt (28)

In the above equation (25), T _EGR is the temperature of the recirculated exhaust gas that flows through the EGR pipe 46 and flows into the intake pipe 34. In the above formula (26), T ₀ is the atmospheric temperature. Further, in the above equation (26), ma is the fresh air flow rate newly flowing into the intake pipe 34, and using the intake gas flow rate mc ^i-1 and the recirculated exhaust gas flow rate m _EGR at the previous calculation step, It can be expressed as the following formula (29).
ma = mc ^i-1 −m _EGR (29)

In the above formula _{(27), F EGR} ⁱ is the EGR rate, expressed as the following equation (30) using the fresh air amount Ma ⁱ and recirculated exhaust gas amount _{M EGR} ^i.
F _EGR ⁱ = M _EGR ⁱ / (Ma ⁱ + M _EGR ⁱ ) (30)

Here, in the above formula (30), the fresh air amount Ma ⁱ is remaining in the intake pipe 34 and the fresh air that has flowed during this calculation step, without being sucked into a by the cylinder fresh air at the time of the previous calculation step Can be represented by the following formula (31). Similarly, the recirculated exhaust gas amount M _EGR ⁱ is the exhaust gas recirculated at the current calculation step, the exhaust gas at the previous calculation step, and the exhaust gas remaining in the intake pipe 34 without being sucked into the cylinder. Can be represented by the following formula (32). In the following formulas (31) and (32), Vm represents the volume of the downstream side intake pipe section, and R represents the gas constant.
Ma ⁱ = {Pm · Vm / (R · Tm ^i-1 ) −mc ⁱ⁻¹ · Δt} · (1-F _EGR ⁱ⁻¹ ) + ma · Δt (31)
M _EGR ⁱ = {Pm · Vm / (R · Tm ^i-1 ) −mc ⁱ⁻¹ · Δt} · F _EGR ⁱ⁻¹ + m _EGR · Δt (32)

In the above formula (28), hw is a heat transfer coefficient from the wall surface of the intake pipe 34 to the gas in the pipe, and a Reynolds number (Re = d · u / ν) as a function of the flow velocity u and the kinematic viscosity ν. It is determined by the Prandtl number Pr showing the gas property value characteristic, the thermal conductivity λ of the gas, and the Nusselt number α which is a function of the Reynolds number. Therefore, the heat transfer coefficient hw can be expressed by the following formula (33), where β and δ are constants.
hw = λ · α · Re ^β · Pr ^δ / d (33)

Here, the flow velocity of the gas in the downstream side intake pipe portion can be considered to be a value obtained by dividing the volume flow rate by the cross-sectional area of the intake pipe 34. Therefore, when the cross-sectional area of the intake pipe 34 is Ap and the flow velocity of the gas in the downstream intake pipe section is u, the equation of state established in the downstream intake pipe section is modified and expressed as the following expression (34). be able to.
u = R * Tm ^i-1 * mc ^i-1 / (Ap * Pm) (34)

From the above, the downstream intake pipe model M40 has the recirculation exhaust gas flow rate m _EGR , the recirculation exhaust gas temperature T _EGR , and the atmospheric temperature T ₀ , the recirculation exhaust gas flow rate detection means 60, the recirculation exhaust gas temperature detection means 62, and the atmospheric temperature. The fresh air flow rate ma, the EGR rate F _EGR ⁱ , the heat transfer rate hw, the flow rate u, and the intake gas flow rate mc estimated at the previous step, respectively obtained from the above-described equations (29) to (34). Each term on the right side of the equation (24) can be calculated by applying the equation (25) to the equation (28) together with ^i-1 and the intake pipe gas temperature Tm ^i-1 . Therefore, the intake pipe gas temperature Tm ⁱ can be estimated from the above equations (22) and (23) using the Q value calculated from the above equation (24).

(Intake valve model M50)
The intake valve model M50 is based on the following equation (35), the intake pipe pressure Pm, and the intake pipe gas temperature Tm ^{* i} , Tm ^* , the gas flow rate that passes around the intake valve 28, that is, the intake gas sucked into the combustion chamber 22. it is a model to estimate the flow rate mc ^i.
mc ⁱ = α · (a · Pm + b) (35)
In the above equation (35), α is an intake gas flow rate correction coefficient and can be expressed as α = Tm ^{* i} / Tm ⁱ . α is a value smaller than 1, for example, as shown in FIG. 3, the maximum value is 1 at an EGR rate of 0 and becomes smaller as the EGR rate is higher. In the above formula (35), a is a proportional coefficient, and b is a value representing burned gas remaining in the cylinder.

The method of estimating the intake gas flow rate mc ⁱ by the intake valve model M50 is specifically as follows. The intake valve model M50 acquires the intake pipe pressure Pm from the intake pipe pressure detection means 56. Further, the intake pipe gas temperatures Tm ^{* i} and Tm ⁱ are obtained from the upstream intake pipe model M30 and the downstream intake pipe model M40, respectively. At the same time, the intake valve model M50 stores tables defining the relationship between the engine speed Ne, the intake valve opening / closing timing VT, the maximum lift amount Lmax of the intake valve, and the proportionality coefficient a and the burned gas amount b. The proportional coefficient a and the burned gas amount b are obtained from the actual engine speed Ne, the intake valve opening / closing timing VT, the intake valve maximum lift amount Lmax, and the respective tables. Then, these values were applied to the equation (35) obtains the intake gas flow rate mc ⁱ at time t.

  Here, the reason why the above equation (35) describing the intake valve model M50 is employed will be described. As described when the equation (1) is described, the intake gas amount is determined when the intake valve is closed, and is proportional to the in-cylinder pressure at that time. The in-cylinder pressure when the intake valve is closed can be regarded as equal to the pressure upstream of the intake valve, that is, the intake pipe pressure. Therefore, it can be said that the amount of intake gas is proportional to the intake pipe pressure. As described in the description of the downstream intake pipe model M40, when exhaust gas is recirculated into the intake pipe 34, the gas density ρm in the intake pipe 34 changes, and this gas density ρm is inversely proportional to the gas temperature. Are in a relationship. Therefore, in the present embodiment, the above formula (35) that can follow with high accuracy by the change in gas density ρm (change in gas temperature) due to the exhaust gas is employed.

The intake gas flow rate mc ⁱ estimated in this way is integrated over time from the opening timing of the intake valve 28 to the closing timing, so that the intake gas amount Mc taken into the combustion chamber 22 in the intake stroke of the engine 10 is obtained. Can be estimated. Then, the fuel injection amount determining means shown in FIG. 2 determines the fuel injection amount fc by applying the intake gas amount Mc to the above equation (2).

FIG. 4 is a graph showing a change in the intake gas amount with respect to the EGR rate. Of the three curves shown in FIG. 4, Mc (with correction) indicates the intake gas amount Mc when estimated using the above equation (35), and is Mc (without correction). This shows the intake gas amount Mc ^* when estimated using the above equation (1). Further, another curve (measured value) represents the intake pipe pressure Pm, the intake pipe gas temperature Tm * ^i, the intake gas amount obtained by actually measuring the Tm ^i. As can be seen from FIG. 4, the intake gas amount decreases as the EGR rate increases (actual measurement value). Further, since the above formula (1) does not assume that exhaust gas is recirculated, when the above formula (1) is used, the deviation from the actual measurement value increases as the EGR rate increases (Mc (correction None)). On the other hand, when estimated using the above equation (35), the intake gas amount Mc close to the actual measurement value can be estimated (Mc (with correction)).

Next, specific processing for realizing the above-described fuel injection control will be described with reference to FIGS. First, FIG. 5, in this embodiment, is a flowchart showing a calculation procedure of the intake pipe gas temperature Tm ⁱ performed by the ECU 70. The routine shown in FIG. 5 is repeatedly executed during engine operation.

According to the routine shown in FIG. 5, the ECU 70 first reads the recirculation exhaust gas flow rate m _EGR and the recirculation exhaust gas temperature T _EGR (step 100). As described above, since the ECU 70 is connected to the recirculation exhaust gas flow rate detection means 60 and the recirculation exhaust gas temperature detection means 62, the recirculation exhaust gas flow rate m _EGR and the recirculation exhaust gas temperature T _EGR can be read from these. it can.

Subsequently, the ECU 70 reads the intake gas flow rate mc ^i-1 that flowed into the cylinder in the previous step, the intake pipe gas temperature Tm ^i-1, and the intake pipe pressure Pm (step 110). The ECU 70 further includes a storage unit for storing the intake gas flow rate mc ^k estimated in the past and the intake pipe gas temperature Tm ^k (k is a natural number). Therefore, the intake gas flow rate mc ^i-1 and the intake pipe gas temperature Tm ^i-1 which are the previous values can be read from the storage unit. Further, as described above, since the ECU 70 is connected to the intake pipe pressure detection means 56, the intake pipe pressure Pm can be read.

Subsequently, the ECU 70 calculates the fresh air flow rate ma newly flowing into the intake pipe 34 using the recirculated exhaust gas flow rate m _EGR and the intake gas flow rate mc ^i-1 read in steps 100 and 110 (steps). 120). Note that the formula (29) corresponds to the formula used in this step.

Subsequently, the ECU 70 reads the recirculated exhaust gas flow rate m _EGR , the intake gas flow rate mc ^i-1 , the intake pipe gas temperature Tm ^i-1 , the intake pipe pressure Pm read in steps 100 and 110, and the EGR rate calculated in the previous step. The new air amount Ma ⁱ , the exhaust gas amount M _EGR ⁱ , and the EGR rate F _EGR ⁱ are calculated using F _EGR ⁱ⁻¹ as described above (step 130). In addition to the intake gas flow rate mc ^k and the intake pipe gas temperature Tm ^k , the ECU 70 stores an EGR rate F _EGR ^k (k is a natural number) calculated in the past in its storage unit. Therefore, the previous value F _EGR ^i-1 of the EGR rate is read from the storage unit, and the fresh air amount Ma ⁱ , the exhaust gas is obtained using the recirculation exhaust gas flow rate m _EGR , the intake gas flow rate mc ^i-1 , and the intake pipe pressure Pm. The quantity M _EGR ⁱ and the EGR rate F _EGR ⁱ can be calculated respectively. The formulas used in this step correspond to the above formulas (30) to (32). The EGR rate F _EGR ⁱ obtained in this step is stored in the storage unit of the ECU 70 for the next calculation of this routine execution.

Subsequently, the ECU 70 calculates the flow velocity u of the gas in the intake pipe 34 using the intake gas flow rate mc ⁱ⁻¹ , the intake pipe gas temperature Tm ⁱ⁻¹ read in step 110, and the intake pipe pressure Pm. (Step 140). The equation used in this step corresponds to the above equation (34).

  Subsequently, the ECU 70 calculates the heat transfer rate hw from the wall surface of the intake pipe 34 to the gas using the gas flow velocity u calculated in step 140 (step 150). The equation used in this step corresponds to the above equation (33).

Subsequently, ECU 70 reads a wall temperature _{T w} of the intake pipe 34, an upstream temperature _{T O} of the throttle valve 38 (step 160). As described above, ECU 70 is wall temperature detection means 58, since it is connected with the atmosphere temperature detector 52, it can be read them from the wall surface temperature T _w, the upstream temperature T _O of the throttle valve 38, respectively.

Subsequently, ECU 70 is the wall temperature _{T w} read in step 160, another temperature _{T O} of the throttle valve 38, the recirculated exhaust gas flow rate _{m EGR} read in step 100, and recirculated exhaust gas temperature _{T EGR,} calculated in step 120 Using the fresh air flow rate ma, the EGR rate F _EGR ⁱ calculated in step 130, the heat transfer rate hw calculated in step 150, and the like, the heat quantity Q _{EGR of the} exhaust gas, the heat quantity Qa of the fresh air, and the air drawn into the cylinder The amount of heat Qc of the intake gas and the amount of heat transfer Qw from the wall surface of the downstream side intake pipe portion are calculated. Based on the calculated values, the heat transfer amount Q to the intake gas is calculated from the relational expression of the heat balance in the downstream side intake pipe section (step 170). In addition, the said formula (24)-Formula (28) correspond to the formula used at this step.

Finally, the ECU 70 updates the intake pipe gas temperature Tm ⁱ using the fresh air amount Ma ⁱ , the recirculated exhaust gas amount M _EGR ⁱ calculated in step 130, and the heat transfer amount Q to the intake gas calculated in step 160. (Step 180). In addition, the said formula (22) and Formula (23) correspond to the formula used at this step. The intake pipe gas temperature Tm ⁱ obtained in this step is stored in the storage unit of the ECU 70 for the next calculation of this routine execution.

FIG. 6 is a flowchart showing a calculation procedure of the intake pipe gas temperature Tm ^{* i} executed by the ECU 70 in the present embodiment. The routine shown in FIG. 6 is repeatedly executed during the operation of the engine, like the routine shown in FIG.

  According to the routine shown in FIG. 6, first, the ECU 70 estimates the throttle valve opening degree θt, and uses this throttle valve opening degree θt and various tables stored in the ECU 70 to produce a flow coefficient Ct (θt). The opening area At (θt) is obtained (step 200). As described above, the ECU 70 has a table that defines the relationship between the throttle valve opening θt and the flow coefficient Ct (θt) and a table that defines the relationship between the throttle valve opening θt and the opening area At (θt). The flow rate coefficient Ct (θt) and the opening area At (θt) are obtained by applying the throttle valve opening θt to these tables.

Subsequently, the ECU 70 determines the flow coefficient Ct (θt) obtained in step 200, the opening area At (θt), the intake pipe gas temperature Tm ^{* i−1} estimated in the previous step, and the intake pipe pressure Pm ^* estimated in the previous step ^{. i-1,} the upstream temperature _{T O} of the throttle valve 38, with the upstream pressure _{P O} and the like of the throttle valve 38, calculates the throttle passing fresh air flow rate mt ⁱ (step 210). In addition to the intake gas flow rate mc ^{k and the} like, the ECU 70 stores the intake pipe gas temperature Tm ^{* l} and the intake pipe pressure Pm ^{* l} (l is a natural number) calculated in the past. Therefore, the previous value Tm ^{* i−1 of} the intake pipe gas temperature and the previous value Pm ^{* i−1} of the intake pipe pressure can be read from the storage unit. Further, ECU 70 is atmospheric temperature detection means 52, because it is connected to the atmospheric pressure detecting means 54, it is possible to read the upstream temperature _{T O} of the throttle valve 38, the upstream pressure _{P O} of the throttle valve 38 from each of these. The formula used in this step corresponds to the above formula (3) or (4). The throttle passage fresh air flow rate mt ⁱ obtained in this step is stored in the storage unit of the ECU 70 for the next calculation of the routine execution.

Subsequently, the ECU 70 uses the throttle passage fresh air flow rate mt ⁱ⁻¹ , the intake gas flow rate mc ⁱ⁻¹ , and the recirculated exhaust gas flow rate m _EGR calculated in the previous step, and the intake pipe gas temperature Tm ^{* i} and the intake pipe pressure. Pm ^{* i} is obtained (step 220). Here, the recirculation exhaust gas flow rate m _EGR and the intake gas flow rate mc ^i-1 can be read in the same manner as steps 100 and 110 in FIG. In this step, the following formulas (36) and (37) obtained by integrating and discretizing the formulas (17) and (18) are used. The intake pipe gas temperature Tm ^{* i} and the intake pipe pressure Pm ^{* i} obtained in this step are stored in the storage unit of the ECU 70 for the next calculation of this routine.
Pm ^{* i} / Tm ^{* i} = Pm ^{* i−1} / Tm ^{* i−1} + Δt · (R / Vm ^* ) {mt ⁱ⁻¹ − (mc ⁱ⁻¹ −m _EGR ) (36)
Pm ^{* i} = Pm ^{* i−1} + Δt · κ · (R / Vm ^* ) · {mt ⁱ⁻¹ · T ₀ − (mc ⁱ⁻¹ −m _EGR ) · Tm ^{* i−1} } (37 )

7, in this embodiment, is a flowchart showing a calculation procedure of the intake gas flow rate mc ⁱ performed by the ECU 70. The routine shown in FIG. 7 is repeatedly executed during the operation of the engine, like the routine shown in FIG.

According to the routine shown in FIG. 7, ECU 70, first, it reads the intake pipe gas temperature Tm ⁱ from the downstream intake pipe model M40 (step 300). In this step, the ECU 70 reads the intake pipe gas temperature Tm ⁱ updated in step 180 of FIG.

  Subsequently, the ECU 70 reads the intake pipe pressure Pm (step 310). As described above, since the ECU 70 is connected to the intake pipe pressure detection means 56, the intake pipe pressure Pm can be read.

Subsequently, the ECU 70 reads the intake pipe gas temperature Tm ^{* i} (step 320). In this step, the ECU 70 reads the intake pipe gas temperature Tm ^{* i} obtained in step 220 of FIG.

Subsequently, the ECU 70 calculates an intake gas flow rate correction coefficient α from the intake pipe gas temperature Tm ⁱ and the intake pipe gas temperature Tm ^{* i} read in steps 300 and 320, respectively (step 330).

Subsequently, ECU 70 includes an intake pipe pressure Pm read in step 310, the intake gas flow rate correction coefficient α calculated in step 330, using the proportionality coefficient a and the burnt gas quantity b, calculates the intake gas flow rate mc ⁱ ( Step 340). As described above, the ECU 70 stores tables defining the relationship among the engine speed Ne, the intake valve opening / closing timing VT, the maximum lift amount Lmax of the intake valve, and the proportionality coefficient a and the burned gas amount b. ing. Therefore, the proportionality coefficient a and the burned gas amount b can be obtained from the actual engine speed Ne, the intake valve opening / closing timing VT, the intake valve maximum lift amount Lmax, and the respective tables. The equation used in this step corresponds to the above equation (35).

The intake gas flow rate mc ⁱ estimated in this step is integrated over time from the opening timing of the intake valve 28 to the closing timing, so that the intake gas amount Mc that is sucked into the combustion chamber 22 in the intake stroke of the engine 10 is obtained. Can be estimated. The fuel injection amount fc can be obtained by applying the estimated intake gas amount Mc to the above equation (2).

As described above, according to the routine shown in FIGS. 5 to 7, obtains the intake pipe gas temperature Tm ⁱ on the upstream side intake pipe portion in the routine shown in FIG. 5, the intake pipe at the downstream side intake pipe portion in the routine shown in FIG. 6 seeking gas temperature Tm * ^i, it is possible to obtain the intake gas flow rate mc ⁱ using these values in the routine shown in FIG. 7, and a proportional coefficient a and the amount of burned gas b. Thus, if for recirculating exhaust gas into the intake pipe 34, it is possible to the change of the correction of the gas density ρm of the exhaust gas can accurately estimate the intake gas flow rate mc ^i. In particular, when the intake gas flow rate mc ⁱ is estimated, the burned gas amount b only needs to be calculated once, so that it is possible to satisfactorily suppress deterioration in controllability due to an increase in calculation time.

  In the present embodiment, the instantaneous flow velocity is used as the flow velocity u when calculating the Reynolds number Re in the above equation (33), but the average flow velocity during the valve opening period of the intake valve 28 may be used. 8 and 9 are diagrams for explaining a modification of the present embodiment. Specifically, FIG. 8 is a diagram in which the relationship between the crank angle and the intake port flow velocity is associated with the intake valve lift, and FIG. 9 is a diagram illustrating the relationship between the crank angle and the heat transfer coefficient hw.

  As shown in FIG. 8, the gas flow velocity in the intake pipe 34 is an intermittent flow, and the flow velocity is generated only during the opening period of the intake valve 28. As shown in FIG. 9, when the flow rate is slow, the heat transfer rate hw from the wall surface of the intake pipe 34 to the gas in the tube is small, and the heat transfer rate hw increases as the flow rate increases. As described above, the heat transfer coefficient hw is generated mostly during the valve opening period of the intake valve 28 where the flow velocity becomes high, and can be sufficiently ignored during the valve closing period. Therefore, the heat transfer rate hw can also be obtained by using the average flow rate during the valve opening period of the intake valve 28 instead of the instantaneous flow rate. If the average flow velocity during the valve opening period of the intake valve 28 is used, the calculation load can be suppressed as compared with the case where the instantaneous flow velocity is used, and the control interval can be improved because the time interval required for the calculation can be shortened.

  Further, in the present embodiment, the heat transfer amount Qw from the wall surface of the downstream side intake pipe portion is calculated and used from the above equation (28). However, instead of the heat transfer amount Qw, it is averaged over one cycle of the engine 10. The converted heat transfer amount Qwave may be used. FIG. 10 is a diagram for explaining a modification of the present embodiment. As described in the description of FIG. 9, the heat transfer rate hw is generated mostly during the opening period of the intake valve 28 where the flow velocity is high, and can be sufficiently ignored during the closing period. Therefore, if Qwave obtained by averaging the heat transfer amount Qw during the opening period of the intake valve 28 in one cycle is used, the calculation is performed as compared with the case where heat transfer is calculated when the intake valve 28 is opened and closed. Since the load can be suppressed and the time interval required for the calculation can be shortened, the controllability can be improved. Furthermore, instead of the wall surface temperature detection means 58, a heat flow rate sensor from the wall surface of the intake pipe 34 to the intake gas may be installed to calculate the heat transfer amount Qw from the wall surface of the downstream intake pipe section.

Further, in the present embodiment, the recirculation exhaust gas temperature _TEGR is detected by the recirculation exhaust gas temperature detection means 62, but the temperature of the EGR cooler 48 may be substituted. Since the recirculated exhaust gas temperature T _EGR has a correlation with the temperature of the EGR cooler 48 provided for the purpose of cooling the recirculated exhaust gas, the temperature of the EGR cooler 48 can be substituted. Similarly, in the present embodiment, it detects a wall temperature T _w at the wall temperature detecting means 58, a cooling water temperature of the engine 10 may be used as a wall temperature T _w. In this way, the system can be prevented from increasing by substituting the value detected from the detection means existing in the system.

DESCRIPTION OF SYMBOLS 10 Engine 22 Combustion chamber 34 Intake pipe 46 EGR pipe 48 EGR cooler 52 Atmospheric temperature detection means 56 Intake pipe pressure detection means 58 Wall surface temperature detection means 60 Recirculation exhaust gas flow rate detection means 62 Recirculation exhaust gas temperature detection means 70 ECU

Claims (2)

In a control device for an internal combustion engine comprising an intake valve model for calculating an intake gas flow rate sucked into a cylinder using at least a gas temperature and an intake pipe pressure in an intake pipe of the internal combustion engine,
An atmospheric temperature acquisition means for acquiring the atmospheric temperature;
An EGR pipe connecting the exhaust passage of the internal combustion engine and the intake pipe;
Recirculation exhaust gas flow rate acquisition means for acquiring a recirculation exhaust gas flow rate flowing through the EGR pipe;
Recirculation exhaust gas temperature acquisition means for acquiring a recirculation exhaust gas temperature flowing through the EGR pipe;
Applying the intake gas flow rate, the atmospheric temperature, and the recirculated exhaust gas flow rate to the model related to the gas in the intake pipe upstream from the connection with the EGR pipe, the gas temperature in the upstream intake pipe is increased upstream. Upstream gas temperature estimating means for estimating the gas temperature;
Downstream intake pipe pressure acquisition means for acquiring, as a downstream intake pipe pressure, an intake pipe pressure in an intake pipe downstream of a connection portion with the EGR pipe;
Wall surface temperature acquisition means for acquiring the wall surface temperature of the downstream intake pipe;
Applying the atmospheric temperature, the recirculated exhaust gas flow rate, the recirculated exhaust gas temperature, the downstream intake pipe pressure and the wall surface temperature to the model related to the gas in the downstream intake pipe, the gas in the downstream intake pipe Downstream gas temperature estimating means for estimating temperature as downstream gas temperature;
An intake gas flow rate calculating means for calculating an intake gas flow rate to be sucked into a cylinder by applying the upstream gas temperature, the downstream intake pipe pressure and the downstream gas temperature to the intake valve model;
A control device for an internal combustion engine, comprising: An EGR cooler provided in the EGR pipe;
The control apparatus for an internal combustion engine according to claim 1, wherein the recirculation exhaust gas temperature acquisition means acquires the temperature of the EGR cooler as the recirculation exhaust gas temperature.

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