JP2007231757A - Apparatus and method for controlling internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for controlling an internal combustion engine, wherein the apparatus can improve the accuracy of the control of an air-fuel ratio in the internal combustion engine by vaporizing the fuel stuck to an intake valve. <P>SOLUTION: In a control apparatus of the internal combustion engine 1 comprising an injector 11 for supplying fuel to an intake port 4, an ECU 30 acquires the temperature of an intake valve 9 for opening and closing the intake port 4 toward the combustion chamber 8 of the internal combustion engine 1, and regulates the pressure in the intake port 4 by controlling the operation of a variable valve mechanism 20 based on the acquired temperature of the intake valve 9 such that the temperature difference Tc between the temperature on the intake valve 9 and the boiling point of the fuel stuck on the intake valve 9 approaches to the target temperature difference Tt in a critical heat flux point P where the boiling state of the fuel stuck on the intake valve 9 changes from nucleate boiling to transition boiling. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device and a control method for an internal combustion engine including a fuel supply device that supplies fuel to an intake passage.

  From the fuel behavior model, the amount of fuel adhering to intake passage components such as the intake port and the intake valve is obtained, and the amount of fuel adhering to be used for correcting the fuel injection amount is obtained based on the amount of adhering fuel. There is known a fuel injection amount control device for an internal combustion engine that limits the correction of the fuel injection amount by the fuel adhesion correction amount when the intake air intake amount is large when the intake air amount is small (see Patent Document 1). In addition, there is Patent Document 2 as a prior art document related to the present invention.

JP 2003-314329 A Japanese Patent Laid-Open No. 10-77886

  The vaporization of fuel adhering to the intake valve (hereinafter also referred to as adhering fuel) is affected by the heat flux from the intake valve to the adhering fuel, and the amount of adhering fuel that vaporizes increases as the heat flux increases. To do. In the conventional control device, since the fuel adhesion amount is not calculated in consideration of the heat flux from the intake valve to the adhered fuel, the correction of the fuel injection amount may be insufficient. Therefore, the accuracy of air-fuel ratio control of the internal combustion engine may not be sufficient. The heat flux means heat energy that moves per unit area per unit time.

  Therefore, an object of the present invention is to provide a control device and a control method for an internal combustion engine that can improve the accuracy of air-fuel ratio control of the internal combustion engine by quickly vaporizing the fuel adhering to the intake valve. .

  The control apparatus for an internal combustion engine according to the present invention is a control apparatus for an internal combustion engine provided with a fuel supply means for supplying fuel to the intake passage, and controls the temperature of the intake valve that opens and closes the intake passage with respect to the combustion chamber of the internal combustion engine. The intake valve temperature acquisition means to acquire, the temperature difference change means to change the temperature difference between the temperature of the intake valve and the boiling point of the fuel adhering to the intake valve, and the intake valve temperature acquisition means acquired by the intake valve temperature acquisition means Based on the temperature, the temperature difference between the temperature of the intake valve and the boiling point of the fuel adhering to the intake valve is the temperature difference at the critical heat flux point where the boiling state of the fuel adhering to the intake valve changes from nucleate boiling to transition boiling And the operation control means for controlling the operation of the temperature difference changing means so as to approach the target temperature difference, which solves the above-mentioned problem.

  As is well known, the heat flux from the heat transfer surface to the liquid changes according to the boiling state of the liquid. The boiling state of the liquid changes in the order of nucleate boiling, transition boiling, and film boiling as the temperature difference between the heat transfer surface and the liquid boiling point increases, and the heat flux from the heat transfer surface to the liquid changes from nucleate boiling to transition boiling. The maximum value is taken at the changing critical heat flux point. In the control device of the present invention, the temperature difference between the temperature of the intake valve and the boiling point of the attached fuel is brought close to the target temperature difference that is the temperature difference at the critical heat flux point, so the heat flux from the intake valve to the attached fuel is increased, Adhering fuel can be quickly vaporized. Thus, the amount of fuel supplied to the intake passage can be increased to the combustion chamber, so that the accuracy of air-fuel ratio control of the internal combustion engine can be improved.

  In one form of the control device of the present invention, as the temperature difference changing means, a pressure changing means for changing the pressure of the intake passage may be provided (Claim 2), or as the temperature difference changing means, Intake valve temperature raising means for raising the temperature of the intake valve may be provided. The boiling point of the fuel changes according to the pressure around the fuel. For example, the boiling point of the fuel can be reduced by reducing the ambient pressure. Therefore, the boiling point of the attached fuel can be changed by changing the pressure in the intake passage. Therefore, the temperature difference between the temperature of the intake valve and the boiling point of the attached fuel can be changed by changing the pressure of the intake passage or the temperature of the intake valve in this way.

  In one form of the control device of the present invention, a fuel property determination unit that determines the property of the fuel supplied from the fuel supply unit, and a target that corrects the target temperature difference based on a determination result of the fuel property determination unit And a temperature difference correcting means. The boiling point of the fuel is affected by the properties of the fuel, and the heavier the fuel, the higher the boiling point. Therefore, the temperature difference at which the boiling state of the fuel changes from nucleate boiling to transition boiling changes according to the properties of the fuel. In this embodiment, since the target temperature difference is corrected according to the properties of the fuel, the target temperature difference can be matched with the temperature difference at the critical heat flux point of each property fuel. Therefore, the heat flux from the intake valve to the attached fuel can be increased to promote the vaporization of the attached fuel, and the accuracy of air-fuel ratio control of the internal combustion engine can be improved.

  The internal combustion engine control method of the present invention is a control method of an internal combustion engine comprising fuel supply means for supplying fuel to the intake passage, wherein the intake valve opens and closes the intake passage with respect to the combustion chamber of the internal combustion engine. The above-described problem is solved by adjusting at least one of the pressure of the intake passage and the temperature of the intake valve so that the heat flux to the fuel attached to the valve increases (Claim 5).

  According to the control method of the present invention, since at least one of the pressure of the intake passage and the temperature of the intake valve is adjusted so that the heat flux from the intake valve to the attached fuel increases, similarly to the control device of the present invention. Thus, the amount of the fuel supplied to the intake passage can be increased by promoting the vaporization of the adhered fuel. Therefore, the accuracy of air-fuel ratio control of the internal combustion engine can be improved.

  In one embodiment of the control method of the present invention, the temperature difference between the temperature of the intake valve and the boiling point of the fuel attached to the intake valve changes the boiling state of the fuel attached to the intake valve from nucleate boiling to transition boiling. You may adjust at least any one of the pressure of the said intake passage, and the temperature of the said intake valve so that the temperature difference in a limit heat flux point may be approached (Claim 6). Thus, by bringing the temperature difference between the temperature of the intake valve and the boiling point of the attached fuel close to the temperature difference at the critical heat flux point, the heat flux from the intake valve to the attached fuel can be increased.

  As described above, according to the present invention, the heat flux from the intake valve to the attached fuel can be increased and the vaporization of the attached fuel can be promoted, so that the amount of fuel adhering to the intake valve can be reduced. it can. Therefore, it is possible to improve the accuracy of air-fuel ratio control of the internal combustion engine by increasing the amount of fuel led to the combustion chamber among the fuel supplied to the intake passage.

(First form)
FIG. 1 shows a main part of an internal combustion engine in which a control device according to a first embodiment of the present invention is incorporated. An internal combustion engine (hereinafter also referred to as an engine) 1 in FIG. 1 is mounted on a vehicle as a driving power source, and a cylinder block in which a plurality (only one is shown in FIG. 1) of cylinders 2 is formed. 3 and a cylinder head 6 attached to the upper part of the cylinder block 3 and formed with an intake port 4 as an intake passage and an exhaust port 5 as an exhaust passage for one cylinder 2, respectively. A piston 7 is inserted into each cylinder 2 so as to be able to reciprocate. A combustion chamber 8 is formed in each cylinder 2 by the piston 7, the wall surface of the cylinder 2, and the cylinder head 6. Each cylinder 2 is provided with an intake valve 9 for opening and closing the intake port 4 and an exhaust valve 10 for opening and closing the exhaust port 5. Each intake port 4 is provided with an injector 11 as fuel supply means. In addition, since these parts may be the same as that of a well-known engine, detailed description is abbreviate | omitted.

  As shown in FIG. 1, the engine 1 includes a variable valve mechanism 20. The variable valve mechanism 20 includes an intake cam motor 21 and an exhaust cam motor 22 as drive sources, an intake cam mechanism 23 that changes the rotational motion of the intake cam motor 21 into a linear motion that drives the intake valve 9 to open and close, and the rotation of the exhaust cam motor 22. And an exhaust cam mechanism 24 that changes the motion to a linear motion that drives the exhaust valve 10 to open and close. The variable valve mechanism 20 changes the rotational speeds of the intake cam motor 21 and the exhaust cam motor 22 to change valve characteristics such as the valve opening timing, valve closing timing, operating angle, and lift amount of the intake valve 9 and the exhaust valve 10. Can be changed respectively.

  The operation of the variable valve mechanism 20 is controlled by an engine control unit (ECU) 30. The ECU 30 is configured as a computer including a microprocessor and peripheral devices such as a RAM and a ROM necessary for its operation, and controls the operation of the injector 11 and the like by referring to an output signal of a predetermined sensor to operate the engine 1. It is a well-known computer unit for controlling As sensors referred to by the ECU 30, for example, a crank angle sensor 31 that outputs a signal corresponding to the crank angle of the engine 1, an air flow meter 32 that outputs a signal corresponding to the intake amount of the engine 1, and a signal corresponding to the intake air temperature are output. An intake air temperature sensor 33 that outputs a signal corresponding to the temperature of the cooling water of the engine 1, an intake air pressure sensor 35 that outputs a signal corresponding to the pressure of the intake port 4, and a fuel as fuel property determination means A property sensor 36 and the like are provided. The fuel property sensor 36 determines the property of the fuel with reference to, for example, a 50% distillation point that is a temperature at which 50% of the fuel evaporates when the fuel is heated. This 50% distillation point may be detected by, for example, heating a part of the fuel stored in the fuel tank of the engine 1 or detecting a physical quantity correlated with the 50% distillation point. Based on this, the 50% distillation point of the fuel may be estimated.

  Part of the fuel injected from the injector 11 adheres to the intake valve 9. If the amount of the adhered fuel increases, the difference between the amount of fuel injected from the injector 11 and the amount of fuel supplied to the combustion chamber 8 increases, which may reduce the accuracy of air-fuel ratio control of the engine 1. Therefore, the ECU 30 executes the heat flux control routine of FIG. 2 to promote the vaporization of the attached fuel adhering to the intake valve 9. The control routine of FIG. 2 is repeatedly executed at a predetermined cycle while the engine 1 is operating.

  In the control routine of FIG. 2, the ECU 30 first acquires the temperature Tv of the intake valve 9 in step S11. The temperature Tv of the intake valve 9 may be obtained, for example, by providing the intake valve 9 with a temperature sensor that outputs a signal corresponding to the temperature of the intake valve 9 or executing the intake valve temperature calculation routine shown in FIG. You may calculate and acquire by this.

  The intake valve temperature calculation routine of FIG. 3 will be described. In this calculation routine, the amount of heat input and the amount of heat output to the intake valve 9 are calculated, and the temperature of the intake valve 9 is calculated based on the calculated amount of input and output heat. Since the amount of heat transferred from the intake valve 9 to each cylinder 2 is different, the ECU 30 repeatedly executes the control routine of FIG. 3 the same number of times as the number of cylinders 2 of the engine 1 and the intake valves 9 provided in each cylinder 2. The temperature Tv is calculated.

  In step S101 in FIG. 3, the ECU 30 first acquires the intake valve temperature Tv_old calculated when the calculation routine was executed last time. As will be described later, the intake valve temperature Tv calculated by this calculation routine is temporarily stored in the RAM of the ECU 30 or the like. At the cold start, that is, when the engine 1 is stopped and the engine 1 is sufficiently cooled, the temperature of the intake valve 9 is substantially the same as the coolant temperature of the engine 1. Therefore, in the calculation routine that is executed for the first time immediately after the engine 1 is started, that is, executed for the first time after the engine 1 is started, the coolant temperature of the engine 1 is substituted for the intake valve temperature Tv_old. In the subsequent step S102, the ECU 30 acquires various parameters representing the state of the engine 1. As these parameters, for example, the intake air amount, the engine speed, the opening timing of the intake valve 9, the operating angle of the intake valve 9, the lift amount of the intake valve 9, and the like are acquired. The valve operating characteristics of the intake valve 9 such as the valve opening timing, the operating angle, and the lift amount of the intake valve 9 are acquired based on the rotational position of the intake cam motor 21.

  In subsequent steps S103 to S106, the ECU 30 calculates the intake gas heat reception amount Qg, the contact surface heat reception amount Qs, the fuel vaporization latent heat amount Qf, and the combustion gas heat reception amount Qb. The intake gas heat receiving amount Qg is the amount of heat transferred between the intake air flowing into the combustion chamber 8 from the intake port 4 and the intake valve 9, and the temperature difference between the previously calculated temperature Tv_old of the intake valve 9 and the intake air temperature, And the time during which the intake air passes around the intake valve 9 is calculated. The intake gas heat receiving amount Qg may take into account the amount of heat transferred between the blowback gas flowing backward from the combustion chamber 8 to the intake port 4 and the intake valve 9. The contact surface heat receiving amount Qs is a heat amount transferred between the valve seat of the intake valve 9 provided in the cylinder head 6 and the intake valve 9 at the time of sitting, and the previously calculated temperature Tv_old of the intake valve 9 and the intake valve 9 This is calculated based on the temperature difference from the valve seat temperature and the seating time during which the intake valve 9 is seated on the valve seat. The fuel vaporization latent heat amount Qf is the amount of heat taken away when the fuel adhering to the intake valve 9 is vaporized, and is calculated based on the amount of adhering fuel vaporized, the fuel temperature, the fuel vaporization latent heat, and the like. The amount of attached fuel to be vaporized is calculated based on the temperature of the intake valve 9, the pressure of the intake port 4, and the fuel injected from the injector 11. The combustion gas heat reception amount Qb is the amount of heat given from the combustion gas in the combustion chamber 8 to the intake valve 9. The combustion gas temperature in the combustion chamber 8 and the heat of the combustion gas to the intake valve 9 when the intake valve 9 is closed. It is calculated based on the operating time.

  In the next step S107, the ECU 30 calculates the temperature Tv of the intake valve 9 based on the calculated intake gas heat reception amount Qg, contact surface heat reception amount Qs, fuel vaporization latent heat amount Qf, and combustion gas heat reception amount Qb. Specifically, first, the intake heat amount Qg, the contact surface heat reception amount Qs, the fuel vaporization latent heat amount Qf, and the combustion gas heat reception amount Qb, which are calculated, are divided by the specific heat Cv of the intake valve 9 to obtain the intake air. A temperature change ΔTv of the valve 9 is calculated. Thereafter, the temperature change Tv of the intake valve 9 is calculated by adding the temperature change ΔTv to the previously calculated intake valve temperature Tv_old. The calculated intake valve temperature Tv is stored in the RAM of the ECU 30 and used in the control routine of FIG.

  Returning to FIG. 2, the description of the heat flux control routine will be continued. In the next step S12, the ECU 30 calculates the pressure (hereinafter referred to as a target intake pipe pressure) Pt of the intake port 4 that promotes the vaporization of the attached fuel adhering to the intake valve 9. A method for calculating the target intake pipe pressure Pt will be described with reference to FIGS. 4 and 5. FIG. 4 shows an example of the relationship between the temperature difference Tc between the intake valve temperature Tv and the fuel boiling point Tb and the heat flux from the intake valve 9 to the attached fuel. As shown in FIG. 4, as the temperature difference Tc increases, the boiling state of the fuel changes in the order of nucleate boiling, transition boiling, and film boiling, and the heat flux from the intake valve 9 to the attached fuel indicates that the boiling state of the fuel is nucleate boiling. The maximum value is taken at the critical heat flux point P that changes from transition to boiling. Hereinafter, in the present invention, the critical heat flux point P may be referred to as a maximum heat flux point. In order to promote the vaporization of the attached fuel adhering to the intake valve 9, the heat flux from the intake valve 9 to the attached fuel may be increased. On the other hand, the range in which the temperature difference Tc can be adjusted, that is, the temperature range in which the temperature Tv of the intake valve 9 or the boiling point Tb of the fuel can be adjusted is limited. Therefore, in order to increase the heat flux from the intake valve 9 to the adhered fuel while suppressing the temperature difference Tc, the temperature difference Tc is adjusted to a target temperature difference Tt that is a temperature difference at the maximum heat flux point P.

  In order to adjust the temperature difference Tc to the target temperature difference Tt, the boiling point Tb of the attached fuel may be adjusted to the target boiling point Tb_t obtained by subtracting the target temperature difference Tt from the temperature Tv of the intake valve 9. Since the boiling point Tb of the attached fuel is affected by the pressure of the intake port 4, the pressure of the intake port 4 is adjusted to adjust the boiling point Tb of the attached fuel. FIG. 5 shows an example of the relationship between the boiling point Tb of the attached fuel and the pressure of the intake port 4. As shown in FIG. 5, the boiling point Tb of the attached fuel increases as the pressure at the intake port 4 increases. The target intake pipe pressure Pt may be set to the pressure of the intake port 4 at which the temperature difference Tc becomes the target temperature difference Tt. Therefore, referring to FIG. 5, the pressure of the intake port 4 corresponding to the target boiling point Tb_t is set to the target intake pipe pressure Pt. 4 and FIG. 5 is obtained in advance by experiments or the like and stored in the ECU 30 as a map.

  In the next step S13, the ECU 30 adjusts the pressure of the intake port 4 to the target intake pipe pressure Pt. The pressure of the intake port 4 is adjusted by, for example, controlling the operation of the intake cam motor 21 and changing the lift amount of the intake valve 9. When the lift amount of the intake valve 9 is increased during the intake stroke, the flow rate of the intake air flowing through the intake port 4 increases, so the pressure of the intake port 4 decreases. On the other hand, when the pressure of the intake port 4 is increased, the lift amount of the intake valve 9 is decreased. By changing the pressure of the intake port 4 in this way, the variable valve mechanism 20 functions as the pressure changing means and the temperature difference changing means of the present invention. Thereafter, the current control routine is terminated.

  By executing the control routine of FIG. 2, the heat flux from the intake valve 9 to the attached fuel can be increased, so that vaporization of the attached fuel can be promoted and the amount of the attached fuel can be reduced. Therefore, the difference between the amount of fuel injected from the injector 11 and the amount of fuel supplied to the combustion chamber 8 can be reduced. Therefore, the accuracy of the air-fuel ratio control of the engine 1 can be improved.

  The ECU 30 functions as the intake valve temperature acquisition means of the present invention by acquiring the temperature of the intake valve 9 by executing step S11 of FIG. Further, the ECU 30 functions as the operation control means of the present invention by executing step S13 to adjust the pressure of the intake port 4 to bring the temperature difference between the temperature of the intake valve 9 and the boiling point of the attached fuel closer to the target temperature difference. .

(Second form)
A second embodiment of the present invention will be described with reference to FIGS. The control device according to the second embodiment is also applied to the engine 1 shown in FIG. FIG. 6 is a diagram corresponding to FIG. 2 and shows a heat flux control routine executed by the ECU 30. In FIG. 6, the same processes as those in FIG. 2 are denoted by the same reference numerals, and description thereof is omitted. The control routine of FIG. 6 is also repeatedly executed at a predetermined cycle while the engine 1 is operating.

  In the control routine of FIG. 6, the ECU 30 first determines the property of the fuel injected from the injector 11 with reference to the output signal of the fuel property sensor 36 in step S21. The property of the fuel is judged to be heavy when, for example, the 50% distillation point of the fuel is equal to or higher than a predetermined determination temperature set in advance, and is judged to be light when the 50% distillation point of the fuel is lower than the predetermined determination temperature. The relationship between the temperature difference Tc and the heat flux is different between light fuel and heavy fuel. Therefore, a 50% distillation point at which it can be determined that the relationship between the temperature difference Tc used when calculating the target intake pipe pressure Pt and the heat flux needs to be changed is set as the predetermined determination temperature. In the subsequent step S11, the ECU 30 acquires the temperature of the intake valve 9.

  In the next step S22, the ECU 30 calculates a target intake pipe pressure Pt. In this embodiment, the target intake pipe pressure Pt is calculated with reference to FIG. 7 instead of FIG. Since the boiling point of the fuel changes depending on the properties of the fuel, the temperature difference at the maximum heat flux point P at which the boiling state of the fuel changes from nucleate boiling to transition boiling changes according to the properties of the fuel. The line L1 in FIG. 7 shows an example of the relationship between the temperature difference Tc and the heat flux in the light fuel, and the line L2 in FIG. 7 shows an example of the relationship between the temperature difference Tc in the heavy fuel and the heat flux. . Further, a point P1 in FIG. 7 indicates a maximum heat flux point in the case of light fuel, and a point P2 indicates a maximum heat flux point in the case of heavy fuel. In this embodiment, the relationship indicated by the line L1 in FIG. 7 and the relationship indicated by the line L2 are properly used according to the properties of the fuel. In the case of light fuel, the relationship indicated by the line L1 in FIG. The intake pipe pressure Pt is calculated. On the other hand, in the case of heavy fuel, the target intake pipe pressure Pt is calculated using the relationship indicated by the line L2 in FIG. The other procedure for calculating the target intake pipe pressure Pt is the same as the process in step S12 in FIG.

  In subsequent step S13, the ECU 30 adjusts the pressure of the intake port 4 to the target intake pipe pressure Pt. Thereafter, the current control routine is terminated.

  In the control routine of FIG. 6, the relationship between the temperature difference Tc used when calculating the target intake pipe pressure Pt and the heat flux is changed in accordance with the combustion characteristics, so that the intake valve 9 is changed even if the fuel characteristics change. The amount of fuel adhering to can be reduced appropriately. Therefore, the accuracy of the air-fuel ratio control of the engine 1 can be further improved.

  FIG. 7 shows only two types of relationships, ie, the relationship between the temperature difference Tc used in the case of light fuel and the heat flux, and the relationship between the temperature difference Tc used in the case of heavy fuel and the heat flux. The relationship between the temperature difference Tc and the heat flux such as the relationship between the temperature difference Tc and the heat flux in the middle of these is stored in the ECU 30 as a map, and the target intake pipe is used using these relationships. The pressure Pt may be calculated. Further, the position of the line L1 in FIG. 7 is moved in the left-right direction in FIG. 7 according to the 50% distillation point of the fuel, and the target intake pipe pressure Pt may be calculated using the relationship after the movement. . In these cases, the target temperature difference Tt according to the fuel property can be set more appropriately, so that the amount of fuel adhering to the intake valve 9 can be further appropriately reduced.

  The ECU 30 functions as the target temperature difference correction means of the present invention by executing the process of step S22 of FIG. 6 and changing the target temperature difference Tt according to the fuel properties.

(Third form)
A third embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 8, this embodiment is different from FIG. 1 in that the intake valve 9 is provided with an electric heater 40 as an intake valve temperature raising means. Other parts are the same as those in FIG. The electric heater 40 includes a heating wire 41 provided inside the intake valve 9 and a heater controller 42 that adjusts the energization time of the heating wire 41 and the like. The ECU 30 controls the operation of the heating wire 41 via the heater controller 42. FIG. 9 shows a heat flux control routine executed by the ECU 30 of FIG. In FIG. 9, the same processes as those in FIGS. 2 and 6 are denoted by the same reference numerals, and the description thereof is omitted. The control routine of FIG. 9 is repeatedly executed at a predetermined cycle while the engine 1 is operating.

  In the control routine of FIG. 9, the ECU 30 first determines the fuel properties in step S21. In subsequent step S31, the ECU 30 calculates the boiling point Tb of the fuel based on the output signal of the fuel property sensor 36. The boiling point Tb of the fuel has a correlation with the 50% distillation point, and the higher the 50% distillation point, the higher the boiling point Tb of the fuel. Therefore, for example, the relationship between the 50% distillation point and the boiling point Tb of the fuel is obtained in advance through experiments and stored in the ECU 30 as a map, and the boiling point Tb of the fuel is calculated with reference to this map.

  In the next step S32, the ECU 30 calculates a target intake valve temperature Tvt based on the calculated fuel boiling point Tb. At this time, first, the ECU 30 calculates the target temperature difference Tt based on the determined property of the fuel. The target temperature difference Tt is calculated based on the relationship shown in FIG. 7, for example. Specifically, first, it is determined which relationship of line L1 or line L2 in FIG. 7 is used based on the determined property of the fuel, and then the target temperature difference Tt is calculated based on the relationship used. Next, the target intake valve temperature Tvt is calculated by adding the calculated fuel boiling point Tb and the calculated target temperature difference Tt. In subsequent step S33, the ECU 30 controls the operation of the electric heater 40 so that the temperature of the intake valve 9 is adjusted to the target intake valve temperature Tvt. Thereafter, the current control routine is terminated.

  In the third mode, the temperature Tv of the intake valve 9 is adjusted to increase the heat flux from the intake valve 9 to the attached fuel. Also in this embodiment, since the amount of fuel adhering to the intake valve 9 can be appropriately reduced, the accuracy of air-fuel ratio control of the engine 1 can be improved.

  The present invention is not limited to the above-described form and can be implemented in various forms. For example, the means for changing the pressure of the intake port is not limited to the variable valve mechanism. An additional valve may be provided between the intake valve and the throttle valve, and the pressure of the intake port may be adjusted by adjusting the opening of the valve. The variable valve mechanism is not limited to one that drives the cam with an electric motor to open and close the intake valve. Any valve mechanism that can change at least the lift amount of the intake valve may be used.

The figure which shows the principal part of the internal combustion engine in which the control apparatus which concerns on the 1st form of this invention was integrated. The flowchart which shows the heat flux control routine which ECU performs. The flowchart which shows the intake-valve temperature calculation routine which ECU performs. The figure which shows an example of the relationship between the temperature difference of the intake valve temperature and the boiling point of fuel, and the heat flux from the intake valve to the adhered fuel. The figure which shows an example of the relationship between the boiling point of adhering fuel, and the pressure of an intake port. The flowchart which shows the heat flux control routine in 2nd Embodiment. The figure which shows an example of the relationship between the temperature difference and heat flux in 2nd Embodiment. The figure which shows the principal part of the internal combustion engine in which the control apparatus which concerns on the 3rd form of this invention was integrated. The flowchart which shows the heat flux control routine in 3rd Embodiment.

Explanation of symbols

1 Internal combustion engine 4 Intake port (intake passage)
8 Combustion chamber 9 Intake valve 11 Injector (fuel supply means)
20 Variable valve mechanism (temperature difference changing means, pressure changing means)
30 Engine control unit (intake valve temperature acquisition means, operation control means, target temperature difference correction means)
36 Fuel property sensor (Fuel property judging means)
40 Electric heater (temperature difference changing means, intake valve temperature raising means)

Claims (6)

In a control device for an internal combustion engine provided with fuel supply means for supplying fuel to an intake passage,
An intake valve temperature acquisition means for acquiring the temperature of the intake valve that opens and closes the intake passage with respect to the combustion chamber of the internal combustion engine, and a temperature difference between the temperature of the intake valve and the boiling point of the fuel adhering to the intake valve is changed. A temperature difference between the temperature of the intake valve and the boiling point of the fuel adhering to the intake valve based on the temperature of the intake valve acquired by the intake valve temperature acquisition means Operation control means for controlling the operation of the temperature difference changing means so as to approach a target temperature difference that is a temperature difference at a critical heat flux point at which the boiling state of the fuel changed from nucleate boiling to transition boiling. A control device for an internal combustion engine characterized by the above.   2. The control apparatus for an internal combustion engine according to claim 1, wherein pressure changing means for changing the pressure in the intake passage is provided as the temperature difference changing means.   The control apparatus for an internal combustion engine according to claim 1, wherein an intake valve temperature raising means for raising the temperature of the intake valve is provided as the temperature difference changing means.   A fuel property determination unit that determines the property of the fuel supplied from the fuel supply unit; and a target temperature difference correction unit that corrects the target temperature difference based on a determination result of the fuel property determination unit. The control device for an internal combustion engine according to any one of claims 1 to 3. In a control method for an internal combustion engine provided with a fuel supply means for supplying fuel to an intake passage,
At least one of the pressure of the intake passage and the temperature of the intake valve so that the heat flux from the intake valve that opens and closes the intake passage to the fuel adhering to the intake valve increases with respect to the combustion chamber of the internal combustion engine Adjusting the internal combustion engine.   The temperature difference between the temperature of the intake valve and the boiling point of the fuel adhering to the intake valve approaches the temperature difference at the critical heat flux point where the boiling state of the fuel adhering to the intake valve changes from nucleate boiling to transition boiling 6. The method of controlling an internal combustion engine according to claim 5, wherein at least one of the pressure in the intake passage and the temperature of the intake valve is adjusted.

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