JP4508120B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus for an internal combustion engine having a function of estimating the temperature of an intake valve.

  In an internal combustion engine equipped with a port injection valve that injects fuel into the intake port, part of the fuel injected from the port injection valve temporarily adheres to the outside of the intake valve and the rest mixes with fresh air. Then, it is sucked into the cylinder as it is. The fuel adhering to the outside of the intake valve gradually evaporates into the intake port and flows into the cylinder with a delay. When the internal combustion engine is in a steady state, the amount of fuel adhering to the intake valve is balanced at a constant value, and the amount of fuel flowing into the cylinder becomes equal to the amount of injected fuel.

  However, when the internal combustion engine is in a transient operation state, the amount of fuel adhering to the intake valve varies. While this increase / decrease occurs, there is a deviation between the amount of fuel flowing into the cylinder and the amount of fuel injected. Therefore, in the transient operation state, in order to control the amount of fuel sucked into the cylinder with high accuracy, it is required to estimate the evaporation amount of the fuel adhering to the intake valve. Since the fuel evaporation amount from the intake valve depends on the intake valve temperature, in order to accurately estimate the fuel evaporation amount from the intake valve, it is required to estimate the intake valve temperature with high accuracy.

  Japanese Patent Application Laid-Open No. 11-14507 discloses an apparatus for calculating the intake valve temperature based on the combustion gas temperature calculated by the combustion system model. However, this publication does not disclose any specific method for calculating the intake valve temperature based on the combustion gas temperature.

Japanese Patent Laid-Open No. 11-14507 JP-A-8-177556 JP 2000-257467 A JP 11-270399 A

  By the way, the fuel of an internal combustion engine is supplied to the market with different fuel properties depending on the season. For example, generally, light fuel with good volatility is supplied in the cold season, and heavy fuel with reduced volatility is supplied in the hot season. If the fuel properties are different, the calorific value per unit amount is also different, so that the temperature of the combustion gas is also different. For this reason, the amount of heat that the intake valve receives from the gas in the cylinder also changes.

  Further, the intake valve not only receives heat from the gas in the cylinder, but also loses heat of vaporization when the attached fuel evaporates. Therefore, in order to estimate the intake valve temperature with high accuracy, it is necessary to accurately estimate the heat of vaporization taken from the intake valve. If the fuel property is different, the amount of evaporation from the intake valve and the heat of vaporization per unit amount are also different, so the amount of heat of vapor taken from the intake valve also changes.

  In the conventional air-fuel ratio control device, the influence of the fuel property on the intake valve temperature is not considered, and the intake valve temperature cannot be estimated with sufficient accuracy. As a result, particularly in a transient operation state of the internal combustion engine, the air-fuel ratio in the cylinder may not be controlled with sufficient accuracy.

  The present invention has been made to solve the above-described problems, and provides an air-fuel ratio control apparatus for an internal combustion engine that can accurately estimate the intake valve temperature of the internal combustion engine in consideration of the difference in fuel properties. The purpose is to provide.

In order to achieve the above object, a first invention is an air-fuel ratio control apparatus for an internal combustion engine,
Fuel property determining means for determining the fuel property;
Combustion gas heat receiving amount calculating means for calculating the amount of heat received by the intake valve of the internal combustion engine from the combustion gas in the cylinder based on the fuel properties;
Based on the fuel properties, vaporization heat amount calculating means for calculating the amount of heat of vaporization removed from the intake valve when the fuel adhering to the intake valve is vaporized;
Intake valve temperature estimation means for estimating the temperature of the intake valve based on the combustion gas heat reception amount and the vaporization heat amount;
It is characterized by providing.

The second invention is the first invention, wherein
The combustion gas heat receiving amount calculating means includes in-cylinder gas temperature calculating means for calculating a temperature of in-cylinder gas based on the fuel property, and calculating the combustion gas heat receiving amount based on the in-cylinder gas temperature. Features.

The third invention is the first or second invention, wherein
A flowing gas heat receiving amount calculating means for calculating a flowing gas heat receiving amount received from the flowing gas flowing around the intake valve;
A total heat reception amount calculating means for calculating a total heat reception amount received by the intake valve based on the combustion gas heat reception amount, the flowing gas heat reception amount, and the vaporization heat amount;
A temperature change amount calculating means for calculating a temperature change amount of the intake valve based on the total heat receiving amount;
An initial temperature estimating means for estimating an initial temperature of the intake valve;
Further comprising
The intake valve temperature estimation means estimates the temperature of the intake valve based on the initial temperature and the temperature change amount.

Moreover, 4th invention is set in 3rd invention,
The intake valve includes a contact surface heat receiving amount calculation means for calculating a contact surface heat receiving amount received by transmission from the valve seat,
The total heat receiving amount calculating means sets the value obtained by adding the contact surface heat receiving amount to the heat receiving amount calculated based on the combustion gas heat receiving amount, the flowing gas heat receiving amount, and the vaporization heat amount, as the total heat receiving amount. Features.

The fifth invention is the third or fourth invention, wherein
The flowing gas heat receiving amount calculating means includes:
Intake gas heat receiving amount calculating means for calculating an intake gas heat receiving amount generated due to the intake gas flowing from the intake port into the cylinder;
Blow-back heat reception amount calculation means for calculating a blow-back heat reception amount generated due to the blow-back gas flowing backward from the cylinder to the intake port;
A final heat receiving amount calculating means for calculating the flowing gas heat receiving amount based on the intake gas heat receiving amount and the blow back heat receiving amount;
It is characterized by including.

According to a sixth invention, in any one of the first to fifth inventions,
A fuel injection amount for setting the air-fuel ratio in the cylinder to the target air-fuel ratio by estimating the behavior of the fuel adhering to the intake valve based on the temperature of the intake valve estimated by the intake valve temperature estimating means An injection amount calculating means for calculating

  According to the first invention, the temperature of the intake valve is determined based on the amount of heat received by the intake valve of the internal combustion engine from the combustion gas in the cylinder and the amount of heat generated when the fuel adhering to the intake valve is vaporized. Can be estimated. And in the estimation, the influence by the difference in fuel properties can be reflected in the amount of heat received by the combustion gas and the amount of heat of vaporization. For this reason, according to the first aspect, the influence of the fuel property can be taken into consideration, so that the temperature of the intake valve can be estimated with extremely high accuracy.

  According to the second aspect of the invention, it is possible to calculate an accurate in-cylinder gas temperature in consideration of the influence due to the difference in fuel properties. Then, based on the in-cylinder gas temperature, the amount of combustion gas heat received can be calculated with high accuracy.

  According to the third invention, in addition to the combustion gas heat reception amount and the vaporization heat amount, the flow gas heat reception amount that the intake valve receives from the flow gas flowing therearound is calculated, and then the total heat reception amount is calculated based on them. be able to. For this reason, according to the third aspect, the influence of the flowing gas can be accurately reflected in the intake valve temperature, and the intake valve temperature can be estimated with higher accuracy.

  According to the fourth aspect of the invention, the influence of the contact surface heat received by the intake valve from the valve seat can also be reflected in the temperature of the intake valve.

  According to the fifth aspect of the invention, the intake gas heat receiving amount due to the intake gas flowing from the intake port into the cylinder and the blow back heat receiving amount due to the blow back from the cylinder are distinguished and calculated, A flowing gas heat receiving amount can be calculated. For this reason, according to the fifth aspect of the present invention, the amount of flowing gas heat can be calculated with high accuracy, and as a result, the temperature of the intake valve can be estimated with higher accuracy.

  According to the sixth invention, by estimating the behavior of the fuel adhering to the intake valve based on the estimated intake valve temperature, the fuel injection amount for making the in-cylinder air-fuel ratio the target air-fuel ratio can be accurately determined. Can be calculated. For this reason, the air-fuel ratio in the cylinder can be controlled with high accuracy even in a warm-up process or a transient operation state.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. As shown in FIG. 1, the system according to the first embodiment of the present invention includes an internal combustion engine 10. An intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10.

  An air flow meter 16 for detecting an intake air amount Ga is disposed in the intake passage 12. A throttle valve 18 is disposed downstream of the air flow meter 16. Further, an injector 20 for injecting fuel into the intake port is disposed further downstream of the throttle valve 18.

  The internal combustion engine 10 includes an intake valve 24 for controlling a conduction state between the intake passage 12 and the cylinder 22. A variable valve mechanism 26 is connected to the intake valve 24 as a drive source. The variable valve mechanism 26 can open and close the intake valve 24 while appropriately changing the valve opening timing, the operating angle, and the lift amount.

  An exhaust valve 28 is disposed between the cylinder 22 and the exhaust passage 14. A variable valve mechanism 30 is connected to the exhaust valve 28 as a drive source. The variable valve mechanism 30 can open and close the exhaust valve 28 while appropriately changing the valve opening timing, the operating angle, and the lift amount.

  In the system of this embodiment, as described above, the intake valve 24 and the exhaust valve 28 are driven by the variable valve mechanisms 26 and 30, respectively, but the mechanism for driving them is not limited to this. Absent. That is, in the system of the present embodiment, the intake valve 24 and the exhaust valve 28 may be driven by a normal cam mechanism.

  The internal combustion engine 10 is equipped with a rotation angle sensor 32 for detecting the engine speed Ne, a water temperature sensor 34 for detecting the cooling water temperature Tw, and an intake pressure sensor 36 for detecting the intake pipe pressure Pm. Yes. The system of this embodiment includes an ECU (Electronic Control Unit) 40. The ECU 40 is supplied with outputs from various sensors including the air flow meter 16 and the rotation angle sensor 32. The ECU 40 can control various actuators including the injector 20 and the variable valve mechanisms 26 and 30 based on the sensor outputs.

  Further, the system of the present embodiment includes a fuel property sensor 38 that detects the property of the fuel supplied to the internal combustion engine 10. The fuel property sensor 38 of the present embodiment is a sensor that detects the volatility of the fuel. The location of the fuel property sensor 38 can be in the fuel tank or in the middle of the fuel passage from the fuel tank to the injector 20.

  In general, the market is supplied with light fuel with good volatility in the cold season and heavy fuel with reduced volatility during the hot season. The ECU 40 can determine the degree of lightness / heavyness of the fuel supplied to the internal combustion engine 10 based on the output of the fuel property sensor 38.

[Intake Valve Temperature Estimation Method in Embodiment 1]
During operation of the internal combustion engine 10, fuel is injected into the intake port by the injector 20. Part of the fuel injected from the injector 20 adheres to the outside of the intake valve 24. The fuel adhering to the outside of the intake valve 24 gradually evaporates into the intake port and flows into the cylinder 22 with a delay. When the internal combustion engine 10 is in a steady operation state, the amount of fuel newly attached to the intake valve 24 and the amount of fuel evaporated from the intake valve 24 are balanced, and the amount of fuel flowing into the cylinder 22 is determined by the injector 20. It becomes equal to the quantity of fuel injected from.

  However, when the internal combustion engine is in a warm-up process or in a transient operation state, the amount of fuel adhering to the intake valve 24 increases or decreases. For this reason, a deviation occurs between the amount of fuel flowing into the cylinder 22 and the amount of fuel injected from the injector 20. For this reason, in order to accurately control the air-fuel ratio in the cylinder 22, it is required to accurately grasp the amount of fuel flowing into the cylinder 22.

  In order to accurately grasp the amount of fuel flowing into the cylinder 22, it is necessary to accurately estimate the behavior of the fuel adhering to the intake valve 24. Specifically, it is necessary to accurately estimate the ratio between the amount evaporated from the intake valve 24 and the amount remaining in the intake valve 24. In order to accurately perform the estimation, it is necessary to accurately estimate the temperature of the intake valve 24. In view of this, the system of the present embodiment estimates the temperature of the intake valve 24 by the method described below.

  2A and 2B are diagrams for explaining the principle by which the system of the present embodiment calculates the temperature Tv of the intake valve 24. FIG. More specifically, FIG. 2 (A) is a diagram for explaining the thermal environment of the intake valve 24 during valve closing. FIG. 2B is a view for explaining the thermal environment of the intake valve during valve opening.

  Symbols Qb, Qs, and Qf shown in FIG. 2A indicate the combustion gas heat reception amount, the contact surface heat reception amount, and the fuel vaporization heat amount, respectively. The combustion gas heat reception amount Qb is the amount of heat given from the combustion gas in the cylinder 22 to the intake valve 24. The contact surface heat receiving amount Qs is the amount of heat transferred to the intake valve 24 from the mechanical contact surface with the valve seat. Further, the fuel vaporization heat quantity Qf is a heat quantity taken away when the fuel adhering to the intake valve 24 is vaporized. As shown in FIG. 2A, during the closing of the intake valve 24, the above-described three types of heat are mainly transferred between the intake valve 24 and its surroundings.

  Symbols Qgin and Qgback shown in FIG. 2B indicate the intake gas heat reception amount and the blowback heat reception amount that are generated when the intake valve 24 is opened. The intake gas heat receiving amount Qgin is the amount of heat transferred between the fresh air flowing into the cylinder 22 from the intake port and the intake valve 24. On the other hand, the blowback heat reception amount Qgback is a heat reception amount generated due to the blowback gas flowing backward from the cylinder 22 to the intake port while the intake valve 24 is opened. As shown in FIG. 2B, during the opening of the intake valve 24, these two types of heat are mainly transferred between the intake valve 24 and its surroundings. Hereinafter, these heat reception amounts are collectively referred to as “fluid gas heat reception amount”.

  The temperature of the intake valve 24 rises by absorbing heat from the surrounding environment, and falls by releasing heat to the surrounding environment. For this reason, if the initial temperature of the intake valve 24 is known, it is possible to estimate the temperature of the intake valve 24 by detecting the total amount of heat received thereafter. And in order to perform the estimation with high accuracy, it is effective to detect the five types of heat amounts described above with high accuracy. In particular, since the flowing gas heat receiving amounts Qgin and Qgback shown in FIG. 2B vary greatly depending on the operating state of the internal combustion engine 10, the values are accurate to estimate the intake valve temperature Tv with high accuracy. It is important to ask for.

  Therefore, in the present embodiment, based on the operating state of the internal combustion engine 10, three types of heat receiving amounts Qb, Qs, Qf shown in FIG. 2A and flowing gas heat receiving amounts Qgin, Qgback shown in FIG. Are calculated separately, and the total amount of heat received by the intake valve 24 is accurately calculated by integrating them. Then, the intake valve temperature Tv is accurately estimated based on the total amount of heat received thus calculated.

  Also, if the fuel properties are different, the vaporization speed, the heat of vaporization per unit amount, the amount of heat generated when burned, and the like are different. For this reason, some of the amounts of heat received are affected by the fuel properties. Therefore, in the present embodiment, the fuel property is detected by the fuel property sensor 38, and the influence of the detected fuel property is taken into consideration, so that the intake valve temperature Tv is estimated with higher accuracy.

[Specific Processing in Embodiment 1]
FIG. 3 is a flowchart of a routine executed in the present embodiment in order to realize the above function. The routine shown in FIG. 3 is started when the internal combustion engine 10 starts. Here, first, the coolant temperature Tw at that time is set as the initial value of the intake valve temperature Tv (step 101). When the internal combustion engine 10 is stopped for a sufficiently long time, the intake valve temperature Tv converges to the temperature of the internal combustion engine 10, that is, the cooling water temperature Tw. For this reason, when the internal combustion engine 10 is started, the process of step 101 can be performed to accurately estimate the intake valve temperature Tv.

  Next, various parameters representing the current state of the internal combustion engine 10 are measured (step 102). Specifically, in addition to the intake air amount Ga, the engine speed Ne, the engine load KL, and the air-fuel ratio A / F, the state of the variable valve mechanism 26 (the valve opening timing VT of the intake valve 24, the lift amount) VL and working angle Vθ) are detected. As the air-fuel ratio A / F, a target air-fuel ratio value set by the ECU 40 or an exhaust air-fuel ratio value detected by an air-fuel ratio sensor (not shown) arranged in the exhaust passage 14 can be used. .

  Subsequent to the processing of step 102, based on the output of the fuel property sensor 38, the property of the fuel supplied to the internal combustion engine 10, that is, the degree of lightness / heavyness of the fuel is determined (step 103).

  Next, the temperature (representative temperature) Tc of the gas in the cylinder 22 is calculated by the method described below (step 104). The in-cylinder gas temperature Tc is used as a basis for obtaining the combustion gas heat receiving amount Qb and the like as will be described later.

The in-cylinder gas temperature Tc changes according to the operating conditions of the internal combustion engine 10. Therefore, the in-cylinder gas temperature Tc can be obtained as a function of the operating conditions of the internal combustion engine 10. In the present embodiment, the in-cylinder gas temperature Tc is calculated using the following arithmetic expression as a function thereof.
Tc = K1 * A / F + K2 * Ne + K3 * KL + K4 * Ga + K5 * VT + K6 * Vθ (1)

  In the above equation (1), A / F is the air-fuel ratio, Ne is the engine speed, Ga is the intake air amount, VT is the opening timing of the intake valve 24, Vθ is the operating angle of the intake valve 24, and K1 to K6 are predetermined Is the coefficient.

  If the fuel properties are different, the amount of heat generated when a unit amount of fuel burns also differs. FIG. 4A is a diagram showing the relationship between the fuel property and the calorific value. As shown in the figure, in the present embodiment, the lighter the fuel property, the greater the amount of heat generated. Note that the relationship between the fuel property and the calorific value differs depending on the type of fuel and the like, and therefore the relationship as shown in FIG.

  If the amount of heat generated by the fuel varies depending on the difference in fuel properties, the in-cylinder gas temperature Tc also varies. That is, the in-cylinder gas temperature Tc varies depending on the fuel properties. For this reason, the combustion gas heat receiving amount Qb calculated based on the in-cylinder gas temperature Tc is also affected by the fuel properties.

  Therefore, in this embodiment, the in-cylinder gas temperature Tc is calculated in consideration of the influence of fuel properties. The influence of the fuel property can be added to the calculated value of the in-cylinder gas temperature Tc by changing the coefficients K1 to K6 in the equation (1) according to the fuel property. Therefore, in the present embodiment, the relationship between each of the coefficients K1 to K6 and the fuel properties is investigated in advance, and a map corresponding to the relationship is stored in the ECU 40. When calculating the in-cylinder gas temperature Tc, the coefficients K1 to K6 are first acquired by comparing the fuel property information acquired in step 103 with those maps. Then, the in-cylinder gas temperature Tc is calculated according to the above equation (1) using the acquired coefficients K1 to K6 and the operating condition parameter acquired in step 102. By such a method, in step 104, an accurate in-cylinder gas temperature Tc can be obtained in consideration of the influence of fuel properties.

  Subsequent to the process of step 104, it is determined whether or not the amount of blowback that occurs when the intake valve 24 is opened is greater than the determination value α (step 105). The blowback amount can be estimated based on the state of the internal combustion engine 10, specifically, for example, based on the load KL of the internal combustion engine 10, the valve overlap amount VOL, the engine speed NE, and the like.

  FIGS. 5A to 5C are diagrams showing the relationship between the blowback amount, the load KL, the valve overlap VOL, and the engine speed NE. In the present embodiment, the ECU 40 stores a map corresponding to these relationships. In step 105, the map is referenced to estimate the amount of blow-back that is predicted to occur under the current situation, and it is further determined whether the estimated value is greater than a predetermined determination value α.

  The determination value α is a value for determining whether or not it is necessary to consider the blow back heat reception amount Qgback when obtaining the flowing gas heat reception amount. That is, it is a value for judging whether or not a large amount of blowback has occurred, and it is necessary to consider the blowback heat reception amount Qgback. Therefore, when it is recognized that the blowback amount> α is not satisfied, that is, when the blowback amount is equal to or less than the determination value α, it can be determined that it is not necessary to consider the influence of the blowback when estimating the flowing gas heat receiving amount. In this case, after calculating the intake gas heat receiving amount Qgin, the value is directly used as the flowing gas heat receiving amount (step 106). Hereinafter, the flowing gas heat receiving amount obtained here will be represented by the sign “Qg”.

  On the other hand, if it is determined in step 105 that the blowback amount> α is established, it can be determined that the influence of the blowback needs to be taken into account when obtaining the flowing gas heat receiving amount. In this case, the intake gas heat receiving amount Qgin and the blow back heat receiving amount Qgback are calculated, and the sum of these is set as the flowing gas heat receiving amount (step 107). Hereinafter, the flowing gas flow heat quantity obtained here will be denoted by the sign “Qg ′”.

(Example of calculation method for intake gas heat reception Qgin)
The intake gas heat receiving amount Qgin described above can be calculated by, for example, the following arithmetic expression.
Qgin = hgin ・ (Tin−Tv) ・ dtin
hgin = 0.0404 ・ (kg / Dv) ・ Revin ^0.868・ (Dv / liftv) ^0.275
Revin = (ρg ・ Ug ・ Dv) / μg (2)

  However, in the upper equation, hgin is a heat transfer coefficient and can be obtained by the intermediate equation. Further, Tin is the temperature of the intake gas, Tv is the intake valve temperature, and dtin is the time during which the intake gas is circulating around the intake valve 24. Tin can be substituted by the intake air temperature. As the Tv, an estimated value of the current intake valve temperature can be used. Dtin can be obtained based on the engine speed Ne, the lift amount VL of the intake valve 24, the operating angle Vθ, and the like.

  In the middle equation, kg is the heat transfer coefficient of the intake gas, and Dv is the diameter of the intake valve 24. These are all known values. Further, liftv is the lift amount of the intake valve 24 and can be detected from the state of the variable valve mechanism 26 in the present embodiment. Revin is a value defined by the lower equation.

  In the lower equation, ρg is the gas density of the intake port, and Ug is the gas flow rate of the intake port. ρg and Ug can be calculated by a known method based on the temperature of the intake port, the intake air amount Ga, the intake pipe pressure Pm, and the like. Further, μg is a viscosity coefficient of inhaled gas, which is a known value. Therefore, the intake gas heat receiving amount Qgin can be obtained by calculation using the above equation (2).

(Example of calculation method for blowback heat reception Qgback)
The blow back heat receiving amount Qgback can be calculated by, for example, the following arithmetic expression.
Qgback = hgback ・ (Tback−Tv) ・ dtback
hgback = 1.2 · (kg / liftv) · Revback ^0.38 · (2 · liftv / Dv) ^0.62
Revback = (ρg ・ Ug ・ liftv) / μg (3)

  However, in the upper equation, hgback is a heat transfer coefficient and can be obtained by the intermediate equation. Tback is the temperature of the blowback gas, and dtback is the time during which blowback occurs around the intake valve 24. Tback can be substituted by the in-cylinder gas temperature Tc. Further, dtback can be obtained based on the engine speed Ne, the valve opening timing VT of the intake valve 24, the lift amount VL, the working angle Vθ, and the like.

  In the middle equation, kg is the heat transfer coefficient of the blown-back gas, and Dv is the diameter of the intake valve 24. These are all known values. Further, liftv is the lift amount of the intake valve 24 and can be detected from the state of the variable valve mechanism 26 in the present embodiment. Revback is a value defined by the lower equation.

  In the lower equation, ρg is the gas density of the intake port, and Ug is the gas flow rate of the intake port. ρg and Ug can be calculated by a known method based on the temperature of the intake port, the intake air amount Ga, the intake pipe pressure Pm, and the like. Further, μg is a viscosity coefficient of inhaled gas, which is a known value. For this reason, the blow-back heat receiving amount Qgback can be obtained by calculation using the above equation (3).

  The flowing gas heat receiving amount Qg to be obtained in the step 106 can be calculated by using the above equation (2). Further, the flowing gas heat receiving amount Qg ′ to be obtained in the above step 107 can be obtained by adding the calculation result of the above formula (2) and the calculation result of the above formula (3). In this way, the flowing gas heat receiving amount can be calculated by calculation both when the influence of blowback is not taken into account (Qg) and when the influence is taken into account (Qg ′).

(Examples of other calculation methods for fluid gas heat received Qg, Qg ')
However, the method for obtaining the flowing gas heat receiving amounts Qg and Qg ′ is not limited to the method using the arithmetic expression as described above. That is, the flowing gas heat receiving amount Qg that does not consider the influence of blowback can be mapped in advance using the engine speed Ne, the engine load KL, the valve opening timing VT of the intake valve 24, and the like as parameters. Similarly, it is possible to map the flowing gas heat receiving amount Qg ′ in consideration of the blowback effect in advance. For this reason, after these maps are stored in the ECU 40 in advance, in steps 106 and 107, the flow gas heat receiving amount Qg or Qg ′ may be obtained by referring to these maps.

(Calculation of contact surface heat reception Qs)
In the routine shown in FIG. 3, the contact surface heat receiving amount Qs is then calculated (step 108). The contact surface heat receiving amount Qs can be calculated by, for example, an arithmetic expression shown below.
Qs = hs ・ (Tvs−Tv) ・ dts
hs = 4130 · (Pm / 50000) ^0.6 (4)

  However, in the upper equation, hs is a heat transfer coefficient and can be obtained by the lower equation. Tvs is the temperature of the valve seat, and can be substituted by the cooling water temperature Tw. Dts is the time during which the intake valve 24 is seated on the valve seat, and can be calculated based on the engine speed Ne and the operating angle Vθ of the intake valve 24 here. Pm in the lower equation is the intake pipe pressure.

  The contact surface heat receiving amount Qs can be obtained by calculation using the state of the internal combustion engine 10 as a parameter by using the above equation (4). Therefore, in step 108, the contact surface heat receiving amount Qs can be accurately obtained.

  However, the method for obtaining the contact surface heat receiving amount Qs is not limited to the method using the arithmetic expression as described above. That is, the amount of heat per unit time that the intake valve 24 receives from the valve seat is a value that is almost uniquely determined with respect to the difference ΔT between the valve seat temperature and the intake valve temperature Tv. The time during which the intake valve 24 is seated on the valve seat is a function of the engine speed Ne and the operating angle Vθ of the intake valve 24. For this reason, the contact surface heat receiving amount Qs can be mapped in advance using the temperature difference ΔT, the engine speed Ne, and the operating angle Vθ as parameters. Therefore, in step 108, the contact surface heat receiving amount Qs may be obtained based on the map.

(Calculation of fuel vaporization heat quantity Qf)
Next, in the routine shown in FIG. 3, the fuel vaporization heat quantity Qf is calculated (step 109). The fuel vaporization heat quantity Qf can be calculated by, for example, an arithmetic expression shown below.
Qf = mf · {(Tv−Tf) · Cpf + Hf} · dtf (5)

  In the above equation (5), mf is the fuel evaporation amount. Tf is the fuel temperature, and the value can be approximated by a fixed value corresponding to the cooling water temperature at the start, for example. Cpf is the specific heat of fuel, and Hf is the latent heat of fuel vaporization. Dtf is a time to be considered as the fuel vaporization period, and can be set here as a function of the engine speed Ne.

  The fuel evaporation amount mf can be obtained based on the amount of fuel injected toward the intake valve 24, the intake valve temperature Tv, the intake pipe pressure Pm, and the like. The fuel evaporation amount mf is also affected by the fuel properties. FIG. 4B is a diagram showing the relationship between the fuel properties and the fuel evaporation amount mf. As shown in the figure, the fuel evaporation amount mf increases as the lighter fuel with higher volatility increases, and decreases as the heavier fuel with suppressed volatility.

  In the present embodiment, the ECU 40 stores a map corresponding to the relationship as shown in FIG. When calculating the fuel evaporation amount mf, the correction coefficient is first acquired by comparing the fuel property information acquired in step 103 with the map. Then, by multiplying the correction coefficient by the standard fuel evaporation amount obtained based on the amount of fuel injected toward the intake valve 24, the intake valve temperature Tv, the intake pipe pressure Pm, etc., the final result is obtained. A fuel evaporation amount mf is calculated.

  The fuel vaporization latent heat Hf and the fuel specific heat Cpf are determined according to the fuel properties. FIG. 4C is a diagram showing the relationship between the fuel properties and the fuel vaporization latent heat Hf, and FIG. 4D is a diagram showing the relationship between the fuel properties and the fuel specific heat Cpf. As shown in these figures, the fuel vaporization latent heat Hf and the fuel specific heat Cpf are smaller as the fuel property is lighter and larger as the fuel property is heavier. In the present embodiment, the ECU 40 stores a map corresponding to the relationship as shown in FIGS. 4C and 4D. When acquiring the fuel vaporization latent heat Hf and the fuel specific heat Cpf, the fuel vaporization latent heat Hf and the fuel specific heat Cpf are calculated by comparing the fuel property information acquired in step 103 with the maps.

  Thus, the fuel vaporization heat quantity Qf can be obtained by performing the calculation of the above equation (5) based on the state of the internal combustion engine 10 and the fuel properties. Therefore, in step 109, an accurate fuel vaporization heat quantity Qf can be obtained in consideration of the fuel properties in addition to the state of the internal combustion engine 10.

  However, the method for obtaining the fuel vaporization heat quantity Qf is not limited to the method using the arithmetic expression as described above. That is, the fuel vaporization heat quantity Qf can be mapped in advance using the fuel injection quantity, the intake valve temperature Tv, and the fuel property as parameters. Therefore, in step 109, the fuel vaporization heat quantity Qf may be obtained by referring to the map.

(Calculation of combustion gas heat received Qb)
In the routine shown in FIG. 3, next, the combustion gas heat receiving amount Qb is calculated (step 110). The combustion gas heat receiving amount Qb can be calculated by, for example, an arithmetic expression shown below.
Qb = hb ・ (Tc−Tv) ・ dtb
hb = 0.013 · Dc ^−0.2 · Pc ^0.8 · Uc ^0.8 · Tc ^−0.53 (6)

  However, in the upper equation, hb is a heat transfer coefficient and can be obtained by the lower equation. In the upper and lower equations, Tc is the in-cylinder gas temperature described above. In the upper equation, dtb is the time during which the temperature of the combustion gas acts on the intake valve 24, and can be calculated based on the engine speed Ne here.

  In the lower equation, Dc is the cylinder diameter and can be treated as a predetermined value. Pc is the in-cylinder pressure, and can be measured by, for example, an in-cylinder pressure sensor. Uc is the gas flow velocity in the cylinder 22 and can be estimated by a known method based on the operating state of the internal combustion engine 10.

  In this step 110, using the in-cylinder gas temperature Tc calculated in step 104, the combustion gas heat receiving amount Qb is calculated according to the above equation (6). As described above, the in-cylinder gas temperature Tc used here is a value calculated with high accuracy by taking into consideration the influence of fuel properties. Therefore, according to the processing of step 110, an accurate combustion gas heat receiving amount Qb can be obtained in consideration of the influence of the fuel properties.

  However, the method for obtaining the combustion gas heat receiving amount Qb is not limited to the method using the arithmetic expression including the in-cylinder gas temperature Tc as described above. That is, the combustion gas heat reception amount Qb is mapped in advance by using the operating conditions such as the engine speed Ne, the engine load KL, the opening timing VT of the intake valve 24, the fuel injection amount, and the fuel properties as parameters. It is possible to leave. Therefore, in step 110, the combustion gas heat receiving amount Qb may be obtained with reference to the map.

(Renewal of intake valve temperature Tv)
When the above process is completed, an update process for the intake valve temperature Tv is then performed (step 111). Specifically, first, the total heat receiving amount (Qg or Qg ′ + Qs−Qf + Qb) of the intake valve 24 is calculated based on all the heat receiving amounts obtained in the current processing cycle. Next, the total amount of heat received is divided by the specific heat of the intake valve 24 (assumed to be known), thereby calculating a temperature change ΔTv generated during the current processing cycle. Finally, by adding ΔTv to the current intake valve temperature Tv, the intake valve temperature Tv is updated to the latest value.

(Calculation of fuel injection amount and execution of fuel injection)
Once the latest intake valve temperature Tv is obtained as described above, the amount of fuel evaporated from the intake valve 24 and the amount of fuel remaining in the intake valve 24 in the current operation cycle is next based on the intake valve temperature Tv. Are calculated (step 112). This calculation process can be performed using, for example, a known fuel behavior model represented by the adhesion rate / residual rate.

  Once the amount of fuel evaporated from the intake valve 24 and the amount of fuel remaining in the intake valve 24 are calculated, the amount of fuel to be injected from the injector 20 is then calculated based on those values (step 113). Specifically, first, the amount of fuel inflow into the cylinder 22 necessary for setting the air-fuel ratio realized in the cylinder 22 as the target air-fuel ratio is calculated. Next, the amount of fuel that needs to be injected from the injector 20 in order to realize the amount of fuel flowing into the cylinder 22 includes the amount of fuel that evaporates from the intake valve 24 and the amount of fuel that remains in the intake valve 24. Above, it calculates based on a well-known method. When the fuel injection amount is calculated in this way, a process for injecting the calculated amount of fuel from the injector 20 is executed (step 114).

  As described above, according to the routine shown in FIG. 3, the amount of heat received that affects the intake valve temperature Tv includes the flow gas received amount Qg or Qg ′, the contact surface received heat amount Qs, the fuel vaporized heat amount Qf, and the combustion gas received amount. It can be divided into heat quantity Qb and estimated individually.

  In particular, the fuel vaporization heat quantity Qf and the combustion gas heat reception quantity Qb that are easily affected by the fuel properties can be estimated with high accuracy by reflecting the fuel properties detected by the fuel property sensor 38.

  According to such an updating method, various phenomena occurring in the internal combustion engine 10 and further the influence of fuel properties can be finely reflected in the intake valve temperature Tv, and the estimation accuracy can be sufficiently increased. . For this reason, according to the system of the present embodiment, the intake valve temperature Tv can be estimated with extremely high accuracy.

  Further, in the present embodiment, the flowing gas heat receiving amount Qg or Qg ′ can be estimated by further distinguishing between the case where the influence of the blowback should be considered and the case where it is not necessary to consider. Finally, the intake valve temperature Tv can be updated by integrating the amounts of heat received.

  Then, according to the routine shown in FIG. 3, the amount of fuel evaporated from the intake valve 24 and the amount of fuel remaining in the intake valve 24 are extremely reduced by using the intake valve temperature Tv estimated with such extremely high accuracy. It can be obtained with high accuracy. For this reason, even when the internal combustion engine 10 is in a warm-up process or in a transient operation state, the amount of fuel flowing into the cylinder 22 can be accurately calculated. Therefore, the air-fuel ratio in the cylinder 22 can be accurately controlled even in the warm-up process or the transient operation state.

  In the first embodiment described above, the ECU 40 executes the process of step 103, so that the “fuel property determination means” in the first invention executes the processes of steps 104 and 110. When the “combustion gas heat receiving amount calculating means” in the first aspect of the invention executes the processing of step 109, the “vaporization heat amount calculating means” of the first aspect of the invention executes the processing of step 111 above. The “intake valve temperature estimating means” in the invention is realized respectively.

  In the first embodiment described above, the ECU 40 executes the process of step 104, so that the “in-cylinder gas temperature calculating means” in the second aspect of the invention executes the process of step 101. The “initial temperature estimating means” in the third invention executes the process of step 106 or 107, and the “fluid gas heat receiving amount calculating means” in the third invention executes the process of step 111 above. The “total heat receiving amount calculating means” and the “temperature change amount calculating means” in the third invention are realized.

  Furthermore, in the first embodiment described above, the ECU 40 executes the process of step 108, whereby the “contact surface heat receiving amount calculating means” in the fourth invention calculates the intake gas heat receiving amount Qgin in step 106. Accordingly, the “suction gas heat receiving amount calculating means” in the fifth invention calculates the blow back heat receiving amount Qgback in step 107, whereby the “blow back heat receiving amount calculating means” in the fifth invention is determined in step 106 or 107. By calculating the flowing gas heat receiving amount Qg or Qg ′, the “final heat receiving amount calculating means” in the fifth invention performs the processing of steps 112 and 113 to perform the “injection amount calculating” in the sixth invention. Each means is realized.

  In the first embodiment described above, the fuel property sensor 38 is provided and the fuel property is determined based on the output, but the fuel property determination method in the present invention is limited to such a method. is not. For example, in the present invention, a known method may be used in which the fuel property is determined by performing estimation based on the output of a sensor that detects the operating state of the internal combustion engine 10 or the like. As such a fuel property determination method, for example, a method described in JP-A-11-270399 is cited.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure for demonstrating the method in which the system of Embodiment 1 of this invention calculates intake valve temperature Tv. It is a flowchart of the routine performed in Embodiment 1 of the present invention. FIG. 4 is a diagram showing the relationship between fuel properties, heat generation amount, fuel evaporation amount mf, fuel vaporization latent heat Hf, and fuel specific heat Cpf. It is the figure which showed the relationship between the amount of blowbacks, load KL, valve overlap VOL, and engine speed NE.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Intake passage 14 Exhaust passage 24 Intake valve 26, 30 Variable valve mechanism 28 Exhaust valve 38 Fuel property sensor 40 ECU (Electronic Control Unit)

Claims (4)

Fuel property determining means for determining the fuel property;
Combustion gas heat receiving amount calculating means for calculating a combustion gas heat receiving amount received from the combustion gas in the cylinder by the intake valve of the internal combustion engine based on the fuel property;
Based on the fuel properties, vaporization heat amount calculating means for calculating the heat of vaporization removed from the intake valve when the fuel adhering to the intake valve is vaporized;
A flowing gas heat receiving amount calculating means for calculating a flowing gas heat receiving amount received from the flowing gas flowing around the intake valve;
A total heat reception amount calculating means for calculating a total heat reception amount received by the intake valve based on the combustion gas heat reception amount, the flowing gas heat reception amount, and the vaporization heat amount;
A temperature change amount calculating means for calculating a temperature change amount of the intake valve based on the total heat receiving amount;
An initial temperature estimating means for estimating an initial temperature of the intake valve;
Intake valve temperature estimating means for estimating the temperature of the intake valve based on the initial temperature and the amount of temperature change;
With
The flowing gas heat receiving amount calculating means includes:
Intake gas heat receiving amount calculating means for calculating an intake gas heat receiving amount generated due to the intake gas flowing from the intake port into the cylinder;
Blow-back heat reception amount calculation means for calculating a blow-back heat reception amount generated due to the blow-back gas flowing backward from the cylinder to the intake port;
A final heat receiving amount calculating means for calculating the flowing gas heat receiving amount based on the intake gas heat receiving amount and the blow back heat receiving amount;
An air-fuel ratio control apparatus for an internal combustion engine , comprising:   The combustion gas heat receiving amount calculating means includes in-cylinder gas temperature calculating means for calculating a temperature of in-cylinder gas based on the fuel property, and calculating the combustion gas heat receiving amount based on the in-cylinder gas temperature. 2. An air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein The intake valve includes a contact surface heat receiving amount calculation means for calculating a contact surface heat receiving amount received by transmission from the valve seat,
The total heat receiving amount calculating means sets the value obtained by adding the contact surface heat receiving amount to the heat receiving amount calculated based on the combustion gas heat receiving amount, the flowing gas heat receiving amount, and the vaporization heat amount, as the total heat receiving amount. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1 or 2, characterized by the above. A fuel injection amount for setting the air-fuel ratio in the cylinder to the target air-fuel ratio by estimating the behavior of the fuel adhering to the intake valve based on the temperature of the intake valve estimated by the intake valve temperature estimating means The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3 , further comprising an injection amount calculation means for calculating

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