JP2008025374A - Ignition timing control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ignition timing control device suitably control ignition timing and a combustion state of fuel in an internal combustion engine. <P>SOLUTION: The ignition timing control device comprises: an external EGR device recirculating part of exhaust from an internal combustion engine to a combustion chamber; an internal EGR device variably controlling valve timing so as to leave over part of burnt gas in the combustion chamber; an ignition timing acquiring means S103 estimating or detecting actual ignition timing of the fuel; correcting means S106, S107 correcting an internal EGR gas quantity so that the actual ignition timing acquired by the ignition timing acquiring means matches with a target ignition timing, and correcting an external EGR gas quantity so as to offset change in in-cylinder oxygen concentration along with the correction of the internal EGR gas quantity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ignition timing control device for an internal combustion engine.

Since the ignition timing of fuel in an internal combustion engine strongly depends on the state of in-cylinder gas, a technique for controlling the ignition timing of fuel by optimizing the in-cylinder gas state has been proposed. For example, Patent Literature 1 discloses an ignition timing control method that adjusts the in-cylinder temperature by adjusting the amount of EGR gas, thereby matching the ignition timing with a desired ignition timing.
JP 2003-97317 A JP 2005-133601 A JP 2004-150376 A JP 2005-83284 A

  The ignition timing control method disclosed in Patent Document 1 adjusts the EGR gas amount so as to achieve an optimal in-cylinder temperature for the fuel to ignite at the target ignition timing. The in-cylinder oxygen concentration fluctuates, which may affect the combustion characteristics having a strong dependence on the in-cylinder oxygen concentration, such as combustion noise and vibration, exhaust emission, torque fluctuation, and the like.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique capable of more suitably controlling the ignition timing and combustion state of fuel in an internal combustion engine.

  In order to achieve the above object, in the ignition timing control device for an internal combustion engine of the present invention, EGR means for returning a part of the exhaust from the internal combustion engine to the cylinder of the internal combustion engine, and fuel according to the operating state of the internal combustion engine Target ignition timing determining means for determining the target ignition timing, ignition timing acquiring means for acquiring by estimating or detecting the actual ignition timing of fuel, and oxygen concentration acquired by estimating or detecting in-cylinder oxygen concentration The acquisition means and the ignition timing acquired by the ignition timing acquisition means (hereinafter also referred to as “actual ignition timing”) coincide with the target ignition timing, and the oxygen concentration acquired by the oxygen concentration acquisition means (hereinafter “actual oxygen”). In order to prevent the concentration (also referred to as “concentration”) from changing, a configuration including correction means for correcting the amount of exhaust gas returned to the cylinder by the EGR means (hereinafter also referred to as “EGR gas amount”) is employed.

  The ignition timing control device configured as described above is intended to realize an optimum in-cylinder gas state in order to reliably ignite fuel at a desired target ignition timing by adjusting the amount of EGR gas. is there. Specifically, the actual ignition timing is acquired by the ignition timing acquisition means, and if the actual ignition timing and the target ignition timing do not match, the EGR gas amount is corrected so that the actual ignition timing approaches the target ignition timing. Is done. For example, when the actual ignition timing is advanced with respect to the target ignition timing, the EGR gas amount is corrected so that the actual ignition timing moves in the retard direction. The relationship between the required change in actual ignition timing and the correction direction and correction amount of the EGR gas amount is obtained in advance. The target ignition timing is a fuel ignition timing capable of realizing a good fuel state, and is obtained in advance.

Furthermore, in the present invention, the correction of the EGR gas amount is executed under the constraint that the actual oxygen concentration does not vary. In other words, the correction of the EGR gas amount is such that the actual oxygen concentration is E
The process is performed so as to satisfy the condition of not deviating from the target oxygen concentration before the correction of the GR gas amount. The relationship between the required change in the actual ignition timing and the correction direction and correction amount of the EGR gas amount is also determined so as to satisfy this condition.

  Therefore, according to the present invention, an optimal in-cylinder gas state (for example, in-cylinder temperature) for the fuel to ignite at the target ignition timing is realized by correcting the EGR gas amount, and for correcting the EGR gas amount. The fluctuation of the in-cylinder oxygen concentration is suppressed. Therefore, it is possible to control the actual ignition timing to the target ignition timing while suppressing deterioration of various combustion characteristics (for example, combustion noise, vibration, exhaust emission, torque fluctuation, etc.) depending on the in-cylinder oxygen concentration. Become.

  The target ignition timing may be a constant value determined for each operating state of the internal combustion engine, or may be within a range of a constant ignition timing. In the former case, the target ignition timing and the actual ignition timing coincide with each other means that the difference between the actual ignition timing and the target ignition timing is less than a predetermined value. In the latter case, the target ignition timing and the actual ignition timing coincide with each other means that the actual ignition timing is included in “a range of a certain ignition timing”.

  In the present invention, as the EGR means, external EGR means for recirculating a part of the exhaust gas to the cylinder through the EGR passage connecting the exhaust passage and the intake passage of the internal combustion engine, or a part of the burned gas remains in the cylinder. It is possible to employ a configuration having internal EGR means.

  The burned gas remaining in the cylinder by the internal EGR means (hereinafter also referred to as “internal EGR gas”) is a gas immediately after combustion, and its temperature is very high and fluctuates reflecting the operation state of the internal combustion engine. Easy to do. Therefore, the in-cylinder temperature has a tendency to change greatly according to a change in the internal EGR gas amount.

  On the other hand, the exhaust gas recirculated to the cylinder by the external EGR means (hereinafter also referred to as “external EGR gas”) flows through the EGR passage provided outside the exhaust passage and the intake passage, and mixes with the low-temperature intake air. It flows into the cylinder via. Since the temperature of the external EGR gas decreases during this distribution process, the influence of the change in the external EGR gas amount on the in-cylinder temperature tends to be smaller than the temperature of the internal EGR gas.

  In view of the characteristics of the internal EGR gas and the external EGR gas, when correcting the EGR gas amount of the present invention, the ignition timing is controlled by correcting the internal EGR gas amount, and the internal EGR gas amount. It is preferable to cancel the change in the in-cylinder oxygen concentration due to the correction by the correction of the external EGR gas amount.

  Since the ignition timing of fuel strongly depends on the in-cylinder temperature, by optimizing the in-cylinder temperature by appropriately adjusting the amount of internal EGR gas that greatly affects the in-cylinder temperature, the ignition timing is more reliably determined. The target ignition timing can be controlled. At this time, it is conceivable that the in-cylinder oxygen concentration changes due to the correction of the internal EGR gas amount. However, since the external EGR gas amount is corrected so as to cancel out this change in oxygen concentration, the in-cylinder oxygen concentration becomes the in-cylinder temperature. Deviation from the in-cylinder oxygen concentration before the optimization is performed can also be suppressed. At this time, since the influence on the in-cylinder temperature due to the change in the external EGR gas amount is small, the in-cylinder temperature is suitably maintained at the optimum in-cylinder temperature for the fuel to ignite at the target ignition timing. Therefore, according to the above configuration, it is possible to more reliably control the ignition timing to the target ignition timing while suppressing fluctuations in the in-cylinder oxygen concentration.

With the above configuration, the relationship between the required change in the actual ignition timing and the correction direction of the external EGR gas amount and the internal EGR gas amount is as follows. When the actual ignition timing is delayed from the target ignition timing, the internal EGR gas amount is increased and corrected, and the external EGR gas amount is corrected by decreasing the EGR gas amount. Can be.

  When the actual ignition timing is advanced from the target ignition timing, it is considered that the in-cylinder temperature is higher than the optimum temperature. Therefore, if the amount of high-temperature internal EGR gas is reduced to lower the in-cylinder temperature, the actual ignition timing can be corrected in the retarded direction. At this time, it is conceivable that the in-cylinder oxygen concentration increases due to the reduction correction of the internal EGR gas amount. However, if the external EGR gas amount is increased to decrease the in-cylinder oxygen concentration, the internal EGR gas is reduced. The increase in oxygen concentration due to the amount reduction correction can be offset.

  On the other hand, when the actual ignition timing is retarded from the target ignition timing, it is considered that the in-cylinder temperature is lower than the optimum temperature. Therefore, the actual ignition timing can be corrected in the advance direction by increasing the in-cylinder temperature by increasing the amount of high-temperature internal EGR gas. At this time, it is conceivable that the in-cylinder oxygen concentration decreases due to the increase correction of the internal EGR gas amount. However, if the external EGR gas amount is decreased to increase the in-cylinder oxygen concentration, the internal EGR gas is increased. The decrease in oxygen concentration due to the increase correction of the amount can be offset.

  This makes it possible to control the actual ignition timing to the target ignition timing while suppressing fluctuations in the in-cylinder oxygen concentration.

  Here, the ignition timing acquisition means may be a means for acquiring the ignition timing of the fuel by measuring the actual combustion state, or estimating the ignition timing by calculation based on the operating state of the internal combustion engine ( (Predictive) may be used.

  For example, as means for actually obtaining the actual ignition timing by measurement, in-cylinder pressure detection means for detecting in-cylinder pressure is provided, and actual ignition of fuel is performed based on the in-cylinder pressure detected by the in-cylinder pressure detection means. A means for detecting the time can be exemplified.

  The time change of the in-cylinder pressure in the process of fuel ignition and explosion and expansion generally shows a waveform having a sharp peak near the ignition timing. The actual ignition timing can be detected based on the timing corresponding to the peak position. Alternatively, from the measurement result of the in-cylinder pressure, the difference between the change in the in-cylinder pressure due to the compression of the piston without explosion / expansion and the change in the in-cylinder pressure due to the explosion / expansion is detected, and the time change rate of this difference ( It is also possible to detect the actual ignition timing based on time differentiation. In addition, the actual ignition timing can be detected based on the measured value of the in-cylinder pressure by using the correlation between the in-cylinder pressure and the ignition phenomenon of the fuel obtained experimentally or theoretically.

  Then, by performing feedback control of the EGR gas amount based on the actual ignition timing detected in this way, the ignition timing can be controlled to the target ignition timing.

  On the other hand, as means for acquiring the actual ignition timing by estimation based on the operating state of the internal combustion engine, the in-cylinder temperature at the start of the compression stroke (hereinafter also referred to as “initial temperature”) is estimated based on the operating state of the internal combustion engine. Compression that is estimated by at least the initial temperature estimating means, including initial temperature estimating means and temperature change estimating means for estimating a change in the cylinder temperature due to compression in the compression stroke (hereinafter also referred to as “temperature change during compression”). Means for estimating the actual ignition timing based on the in-cylinder temperature at the start of the stroke, the change in the in-cylinder temperature estimated by the temperature change estimation means, and the in-cylinder oxygen concentration acquired by the oxygen concentration acquisition means It can be illustrated.

  According to this configuration, the in-cylinder temperature at the start of the compression stroke in the cycle including the time can be estimated based on the operating state of the internal combustion engine at an arbitrary time, and further, the in-cylinder temperature during the compression stroke can be estimated. Since the change can be estimated, the in-cylinder temperature at an arbitrary time point (crank angle) during the compression stroke can be estimated based on these estimated values.

  It can be determined that the premixed gas has ignited when the in-cylinder temperature satisfies a predetermined condition (for example, when the in-cylinder temperature exceeds a predetermined threshold). Therefore, the time (crank angle) at which the estimated value of the in-cylinder temperature during the compression stroke calculated as described above satisfies the predetermined condition (crank angle) can be estimated as the actual ignition timing.

  As described above, according to the above configuration, when the compression stroke is started under the current operating state of the internal combustion engine, the fuel is surely ignited at a desired timing (that is, the target ignition timing) during the compression stroke. Whether the optimum in-cylinder environment conditions (in-cylinder temperature, in-cylinder oxygen concentration, etc.) can be realized can be estimated by calculation at a stage before the fuel actually ignites.

  Then, by determining whether or not the ignition timing estimated in this way (hereinafter also referred to as “estimated ignition timing”) matches the target ignition timing, the current state of the in-cylinder gas is optimal. Whether or not it is in a state can be determined.

  When the estimated ignition timing and the target ignition timing do not match, the EGR gas amount is corrected so that the estimated ignition timing and the target ignition timing match. The correction direction and correction amount for the EGR gas amount are calculated immediately after the estimated ignition timing is calculated and compared with the target ignition timing as described above, and the EGR gas amount is immediately controlled by the EGR means. Reflected. That is, when the EGR gas amount is corrected and the in-cylinder gas state is optimized before the fuel is actually ignited, the EGR gas amount is controlled by feedback control based on the measurement result of the actual ignition timing. The ignition timing can be controlled with higher accuracy than the above.

  In addition, since the ignition timing is predicted and the EGR gas amount is corrected while reflecting the latest operation state in real time by calculation based on the current operation state of the internal combustion engine, the operation of the internal combustion engine is performed, for example, in a transient operation state. Even in a situation where the state changes from moment to moment, the ignition timing can be controlled more accurately. In particular, when adjusting the ignition timing by correcting the amount of internal EGR gas, the temperature of the internal EGR gas is likely to fluctuate reflecting the operating state of the internal combustion engine, so that the in-cylinder temperature should be optimized with high accuracy during transient operation. However, according to the above configuration, the cylinder temperature can be optimized with high accuracy even in such a case.

  When performing feedback control of the ignition timing based on the actual ignition timing acquired by such estimation calculation, it is possible to improve the control accuracy of the ignition timing by improving the calculation accuracy of the estimated ignition timing by the ignition timing acquisition means. it can. In the said structure, the calculation precision of the estimated ignition timing by an ignition timing acquisition means can be improved by employ | adopting the following structures, for example.

  That is, heat transfer that estimates the amount of heat transfer associated with heat transfer between the intake air temperature detecting means for detecting the temperature of intake air taken into the cylinder and the engine member when the intake air is drawn into the cylinder during the intake stroke A quantity estimation means and an internal EGR heat quantity detection means for detecting the amount of heat of the internal EGR gas. The initial temperature estimation means includes at least the temperature of the intake air detected by the intake air temperature detection means and the heat transfer quantity estimation means. The in-cylinder temperature at the start of the compression stroke may be estimated based on the estimated heat transfer amount and the heat amount of the internal EGR gas detected by the internal EGR heat amount detecting means.

Generally, when intake air (fresh air or a mixture of fresh air and external EGR gas) flowing through the intake passage is sucked into a cylinder during an intake stroke, intake air and various engine members (intake passage, intake manifold, intake air) Heat exchange with a port, an intake valve, a cylinder, a piston, and the like). Depending on the operating state of the internal combustion engine, the temperature of these engine members becomes very high, and therefore, an increase in in-cylinder temperature due to heat exchange between the intake air and these engine members may not be ignored.

  According to the above configuration, the amount of heat transfer accompanying the heat exchange between the intake and the engine member is estimated, and the in-cylinder temperature at the start of the compression stroke is estimated in consideration of this. In addition, the in-cylinder temperature at the start of compression can be estimated. Therefore, since the ignition timing acquisition means can predict the actual ignition timing based on the initial temperature estimated more accurately, the calculation accuracy of the estimated ignition timing can be improved.

  According to the present invention, it is possible to more suitably control the ignition timing and combustion state of fuel in an internal combustion engine.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the ignition timing control apparatus according to the present embodiment is applied and its intake system and exhaust system. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine. A combustion chamber 2 is defined and formed in the cylinder 5 of the internal combustion engine 1 by the upper surface of the piston 3 and the inner wall of the cylinder 5. A fuel injection valve 6 that directly injects fuel into the combustion chamber 2 is provided at the upper portion of the combustion chamber 2.

  The combustion chamber 2 communicates with an intake manifold 21 and an intake pipe 22 upstream thereof via an intake port 20. The combustion chamber 2 communicates with an exhaust manifold 31 and an exhaust pipe 32 downstream thereof through an exhaust port 30.

  The cylinder 5 is provided with an intake valve 23 that opens and closes a connection point between the combustion chamber 2 and the intake port 20 and an exhaust valve 33 that opens and closes a connection point between the combustion chamber 2 and the exhaust port 30. The opening / closing timing of the intake valve 23 and the exhaust valve 33 is variably controlled by the variable valve mechanism 9.

  The internal combustion engine 1 is provided with an EGR device 40 that recirculates part of the exhaust gas to the intake system. The EGR device 40 includes an EGR passage 41 and an EGR valve 42. The EGR passage 41 is a passage connecting the exhaust manifold 31 and the intake manifold 21, and part of the exhaust flows into the intake manifold 21 through the EGR passage 41 and returns to the combustion chamber 2. In this embodiment, the exhaust gas recirculated to the combustion chamber 2 through the EGR passage 41 is referred to as external EGR gas.

  The EGR valve 42 is a flow rate adjustment valve that can change the amount of external EGR gas flowing through the EGR passage 41 by changing the flow passage cross-sectional area of the EGR passage 41. The external EGR gas amount is adjusted by adjusting the opening degree of the EGR valve 42. In the case of the present embodiment, the EGR device 40 corresponds to the external EGR means of the present invention.

The external EGR gas amount may be adjusted by a method other than the opening degree control of the EGR valve 42. For example, in the case of an internal combustion engine equipped with a variable displacement turbocharger, the opening degree of the nozzle vane that changes the flow rate characteristic of the turbine may be adjusted. Further, when the exhaust pipe 32 is provided with an exhaust throttle valve, or when the intake pipe 22 is provided with an intake throttle valve, the opening of the exhaust throttle valve or the intake throttle valve may be adjusted.

  Further, in this embodiment, the opening / closing timing of the intake valve 23 and / or the exhaust valve 33 is variably controlled by the variable valve mechanism 9 so that a part of the burned gas in the combustion chamber 2 is exhausted from the exhaust port 30 or the intake port. Then, the burned gas can be allowed to flow back into the combustion chamber 2 during the intake stroke.

  For example, when the pressure in the combustion chamber 2 or the intake port 20 is lower than the pressure in the exhaust port 30, the valve opening timing of the intake valve 23 is advanced and the intake valve 23 and the exhaust valve 33 are simultaneously opened. By setting the lap period, the burned gas in the combustion chamber 2 can flow into the intake port 20 and can be reintroduced into the combustion chamber 2 in the next intake stroke.

  Alternatively, the burned gas in the combustion chamber 2 is caused to flow into the intake port 20 side by advancing the closing timing of the exhaust valve 33 with respect to the exhaust top dead center, and again in the combustion chamber 2 in the next intake stroke. You may make it introduce.

  Further, the burned gas once discharged to the exhaust port 30 side may be caused to flow back into the combustion chamber 2 in the next intake stroke by delaying the closing timing of the exhaust valve 33 from the exhaust top dead center. .

  In this embodiment, the burned gas remaining in the combustion chamber 2 in this way is referred to as internal EGR gas. The internal EGR gas amount is adjusted, for example, by adjusting the valve overlap period or adjusting the degree of retardation or advance of the intake valve 23 or the exhaust valve 33. In the case of this embodiment, the variable valve mechanism 9 corresponds to the internal EGR means of the present invention.

  The internal combustion engine 1 includes a water temperature sensor 70 that detects the temperature of cooling water that cools the internal combustion engine 1, a crank position sensor 71 that detects the crank angle and the engine speed of the internal combustion engine 1, and a driver who uses the accelerator pedal 7. An accelerator opening sensor 72 that detects an engine load of the internal combustion engine 1 by outputting an electric signal corresponding to the amount of depression, an intake air temperature sensor 73 that detects the temperature of fresh air that flows into the intake pipe 22, and the intake pipe 22 An air flow meter 75 for detecting the flow rate of fresh air is provided. In addition, although illustration and description are omitted in particular, sensors generally provided as a diesel engine are provided.

  The internal combustion engine 1 configured as described above is provided with an ECU 8 that is an electronic control computer that controls the internal combustion engine 1. Each sensor is connected to the ECU 8 through electrical wiring, and an output signal from each sensor is input to the ECU 8. Further, the fuel injection valve 6, the variable valve mechanism 9, and the EGR valve 42 are connected to the ECU 8 through electric wiring, and these devices are controlled in accordance with a command signal output from the ECU 8. Yes. The ECU 8 reads the operating state of the internal combustion engine 1 and the driver's request based on the detection values by these various sensors, and controls the known internal combustion engine 1 such as fuel injection based on them, and controls the ignition timing of the fuel. I do.

  The ignition timing of fuel in the combustion chamber 2 generally depends on the state of the gas in the combustion chamber 2 (hereinafter also referred to as “in-cylinder gas”). In particular, it tends to strongly depend on the temperature of the gas in the combustion chamber 2 (hereinafter also referred to as “in-cylinder temperature”). Therefore, conventionally, a control method of the ignition timing has been proposed in which the in-cylinder temperature is optimized so that the fuel is ignited at a desired ignition timing.

As means for adjusting the in-cylinder temperature, there is a method of operating the EGR gas amount. For example, the temperature of the internal EGR gas is high, and the in-cylinder temperature can be manipulated by adjusting the amount of internal EGR gas. However, when the internal EGR gas amount is adjusted to optimize the in-cylinder temperature,
As the internal EGR gas amount changes, the oxygen concentration of the in-cylinder gas (hereinafter also referred to as “in-cylinder oxygen concentration”) changes, which may cause problems in combustion characteristics depending on the in-cylinder oxygen concentration.

  In contrast, in this embodiment, the internal EGR gas amount is adjusted to optimize the in-cylinder temperature, and the external EGR gas amount is set so as to cancel out the change in the in-cylinder oxygen concentration accompanying the adjustment of the internal EGR gas amount. I try to adjust it. In this way, the in-cylinder temperature is optimized so that the fuel ignition timing is controlled to a desired target ignition timing, and the change in the in-cylinder oxygen concentration is offset and the combustion characteristics that depend on the in-cylinder oxygen concentration are also good. Will be maintained.

  Hereinafter, the ignition timing control performed by the ECU 8 will be described. FIG. 2 is a block diagram showing an outline of ignition timing control in this embodiment.

  In FIG. 2, an area drawn with a broken line represents the ECU 8, and blocks B <b> 1 to B <b> 16 inside the broken line area represent various arithmetic processes executed by the ECU 8. Various sensors and various control target devices drawn outside the ECU 8 are connected to the ECU 8 through the electrical wiring as described above, and communicate detection signals and control signals with the ECU 8. Specifically, a detection signal from the intake air temperature sensor 73 is input to the ECU 8 and used as various intake processes as the intake air temperature. Similarly, the control signal to the EGR valve 42 is the EGR valve opening, the detection signal by the accelerator opening sensor 72 is the accelerator opening, the detection signal by the air flow meter 75 is the intake air amount, and the control to the fuel injection valve 6 is performed. The signal is a fuel injection parameter such as the fuel injection amount and fuel injection timing, the detection signal by the water temperature sensor 70 is the cooling water temperature, the detection signal by the crank position sensor 71 is the crank angle and the engine speed, The control signal is used for various arithmetic processes as valve timings of the intake valve 23 and the exhaust valve 33.

  In block B1, a history of a past fixed cycle (for example, 1000 cycles) of the intake air amount is stored.

  In block B2, a history of past fixed cycles (for example, 1000 cycles) of fuel injection parameters is stored.

  In block B3, the external EGR gas amount and the heat amount of the external EGR gas are calculated based on the EGR valve opening, the intake air amount, the accelerator opening, and the like.

  In block B4, based on the amount of external EGR gas calculated in block B3, the amount of heat of the external EGR gas, the amount of intake air, and the intake air temperature, the mixture of the intake air (fresh air) and the external EGR gas in the intake manifold 21 is determined. The temperature is calculated.

  In block B5, wall surface temperatures of various engine members constituting the intake system are calculated. Here, the wall surface temperatures of the intake manifold 21, the intake port 20, and the intake valve 23 are calculated. Specifically, the wall surface temperatures of the intake manifold 21 and the intake port 20 are approximated by the coolant temperature. The temperature of the intake valve 23 is calculated as a temporary delay system having a certain time constant based on the coolant temperature, the engine speed, the history of the intake air amount and the fuel injection amount in the past fixed cycle.

  In block B6, based on the wall surface temperature of the intake system engine member and the temperature of the air-fuel mixture in the intake manifold 21, the air passes through the intake valve 23 in consideration of the amount of heat transfer from the intake system engine member to the air-fuel mixture. The temperature of the mixture immediately after that is calculated.

Specifically, based on the calculation formula of the heat transfer amount dQ shown in the following formula 1 and the calculation formula of the heat transfer coefficient α shown in the formula 2, it is caused by the heat transfer from the intake system engine member to the air-fuel mixture. The temperature Tgout of the air-fuel mixture after the temperature rise is calculated.

  Here, the calculation formula of the heat transfer coefficient α shown in Equation 2 is to calculate the heat transfer coefficient between the intake system engine member and the air-fuel mixture as a function of the flow velocity and density of the air-fuel mixture, and has been tested in advance. Is required. The flow rate of the air-fuel mixture is calculated based on the engine speed. The density of the air-fuel mixture is calculated based on the intake air amount and the external EGR gas amount.

  In block B7, the internal EGR gas amount and the heat amount of the internal EGR gas are calculated based on the intake air amount, fuel injection amount, engine speed, valve timing, and the like.

  In block B8, the internal EGR gas amount and the heat amount of the internal EGR gas calculated in block B7, and the temperature of the air-fuel mixture immediately after passing through the intake valve 23 calculated in block B6, immediately after passing through the internal EGR gas and the intake valve 23. The temperature of the gas (hereinafter also referred to as “in-cylinder gas”) mixed with the gas mixture (hereinafter also referred to as “in-cylinder temperature”) is calculated. Thus, the temperature rise due to the mixture immediately after passing through the intake valve 23 is mixed with the internal EGR gas remaining in the combustion chamber 2 is calculated.

  In block B9, the wall surface temperature of the engine member constituting the cylinder is calculated. Here, the temperatures of the surface of the piston 3 and the inner wall of the cylinder 5 are calculated. Specifically, the surface temperature of the piston 3 and the inner wall surface temperature of the cylinder 5 are calculated based on the coolant temperature, the history of the fuel injection amount of the past fixed cycle, and the like.

In block B10, based on the wall surface temperature of the cylinder component engine member calculated in block B9 and the temperature of the in-cylinder gas immediately after flowing into the combustion chamber 2 calculated in block B8, the period until the intake stroke is completed The temperature of the in-cylinder gas at the start of the compression stroke is calculated in consideration of the amount of heat transfer from the cylinder constituent engine member to the in-cylinder gas. Here, the amount of heat transfer between the cylinder constituent engine member and the in-cylinder gas is calculated using Equations 1 and 2 in the same manner as in the block B6.

  In block B11, the volume of the combustion chamber 2 at each crank angle during the compression stroke (hereinafter also referred to as “cylinder volume”) is calculated. This may be calculated based on the geometric design of the cylinder 5, or a map for obtaining the in-cylinder volume based on each crank angle may be created in advance and referred to.

  In block B12, in-cylinder for each crank angle during the compression stroke based on the in-cylinder gas temperature at the start of compression calculated in block B10 and the in-cylinder volume for each crank angle calculated in block B11. The temperature of the gas is calculated. Here, the in-cylinder gas temperature at each crank angle is compressed to the in-cylinder volume corresponding to the crank angle with the temperature of the in-cylinder gas at the compression start time calculated in block B10 as the initial temperature. It can be calculated approximately by the temperature change caused by the polytrope change.

  Note that the approximation method is not limited to this. For example, it is possible to calculate the temperature of the in-cylinder gas for each crank angle by calculating the work performed by the piston when the crank angle changes by a minute angle, heat transfer with the cylinder constituent engine member, etc. according to an appropriate physical model. .

  Here, the crank angle interval in the case of “every crank angle” is an interval necessary for performing ignition timing control described later.

  As described above, at an arbitrary time before the actual compression stroke is started, based on the operation state of the internal combustion engine at the time, the in-cylinder temperature when entering the compression stroke in the operation state The change can be predicted in real time by the estimation calculation by the ECU 8.

  In block B13, the oxygen concentration of the in-cylinder gas (hereinafter also referred to as “in-cylinder oxygen concentration”) based on the external EGR gas amount calculated in block B3, the internal EGR gas amount calculated in block B7, and the intake air amount. Is calculated.

  In block B14, the ignition timing of the fuel is calculated based on the in-cylinder temperature calculated in block B12, the in-cylinder oxygen concentration calculated in block B13, and the fuel injection amount.

  In block B15, the target ignition timing is determined based on the operating state of the internal combustion engine. The target ignition timing is an ignition timing at which a good combustion state can be realized in the internal combustion engine 1, is obtained in advance by experiments, and is stored in the ROM of the ECU 8 as a map for determining the target ignition timing according to the operating state of the internal combustion engine 1. ing.

  In block B16, the ignition timing calculated in block B14 (hereinafter also referred to as “estimated ignition timing”) and the target ignition timing determined in block B15 are compared and evaluated.

  Here, if the estimated ignition timing matches the target ignition timing, it is predicted that the fuel will ignite at the desired target ignition timing if the current operating state of the internal combustion engine is maintained and the compression stroke is entered. Therefore, the current engine control state (EGR valve opening degree, valve timing) is maintained.

On the other hand, when the estimated ignition timing is advanced from the target ignition timing, the in-cylinder temperature is decreased by decreasing the internal EGR gas amount in order to move the ignition timing to the retard side. In order to reduce the amount of internal EGR gas, for example, a variable valve mechanism that shortens the period during which both the intake valve 23 and the exhaust valve 33 are closed (hereinafter also referred to as “negative overlap period”). 9 is operated. In this case, since the in-cylinder oxygen concentration slightly increases as the internal EGR gas amount decreases, the external EGR gas amount is increased so as to offset the increase in the in-cylinder oxygen concentration. In order to increase the external EGR gas amount, for example, the opening degree of the EGR valve 42 is operated in the valve opening direction.

  On the other hand, when the estimated ignition timing is retarded from the target ignition timing, the in-cylinder temperature is increased by increasing the internal EGR gas amount in order to move the ignition timing to the advance side. In order to increase the internal EGR gas amount, for example, the variable valve mechanism 9 is operated so as to extend the negative overlap period. In this case, since the in-cylinder oxygen concentration slightly decreases as the internal EGR gas amount increases, the external EGR gas amount is decreased so as to offset the decrease in the in-cylinder oxygen concentration. In order to decrease the external EGR gas amount, for example, the opening degree of the EGR valve 42 is operated in the valve closing direction.

  Thus, in the ignition timing control method of the present embodiment, the in-cylinder temperature is optimized by correcting the internal EGR gas amount, thereby controlling the ignition timing to the target ignition timing and correcting the internal EGR gas amount. It is possible to cancel the fluctuation of the in-cylinder oxygen concentration by correcting the external EGR gas amount, thereby suppressing the deterioration of the combustion state due to the fluctuation of the in-cylinder oxygen concentration.

  In this embodiment, since the internal EGR gas amount and the external EGR gas amount are operated by feedback control based on the comparison between the ignition timing estimated by calculation and the target ignition timing, the operating state of the latest internal combustion engine is changed. This can be reflected in the ignition timing control. Therefore, the ignition timing can be controlled with higher accuracy than when feedback control is performed based on the measurement result of the actual ignition timing. In particular, even in a situation where the operating state of the internal combustion engine changes every moment, such as a transient operating state, the ignition timing can be controlled with higher accuracy.

  In addition, in calculating the estimated ignition timing, the in-cylinder temperature is calculated in consideration of heat transfer between the intake system engine member or cylinder component engine member and the intake or in-cylinder gas. Even in an operating state where the temperature becomes high, the in-cylinder temperature can be calculated with higher accuracy, and therefore the estimated ignition timing can be calculated with higher accuracy.

  Next, a specific procedure for implementing the ignition timing control described above will be described with reference to the flowchart of FIG. The flowchart of FIG. 3 is a flowchart showing a routine for performing the ignition timing control of this embodiment, and this routine is repeatedly executed by the ECU 8 at predetermined intervals.

  First, in step S101, the ECU 8 grasps the operating state of the internal combustion engine 1. Specifically, the detection values of various sensors and control command values to the EGR valve 42, the fuel injection valve 6, the variable valve mechanism 9 and the like are read.

  Next, in step S102, the target ignition timing is determined based on the operating state of the internal combustion engine 1 grasped in step S101. Specifically, the process of block B15 in the block diagram is executed. In the case of the present embodiment, the ECU 8 that executes this step S102 corresponds to the target ignition timing determining means of the present invention.

  Next, in step S103, an estimated ignition timing is calculated based on the operating state of the internal combustion engine 1 grasped in step S101. Specifically, the process of block B14 in the block diagram is executed. In the case of this embodiment, the ECU 8 that executes this step S103 corresponds to the ignition timing acquisition means of the present invention. Moreover, ECU8 which performs calculation of block B13 referred when performing the process of block B14 in this step S103 corresponds to the oxygen concentration acquisition means of this invention.

  Next, in step S104, it is determined whether or not the target ignition timing determined in step S102 matches the estimated ignition timing calculated in step S103. Here, “the estimated ignition timing and the target ignition timing coincide” means that the absolute value of the difference between the estimated ignition timing and the target ignition timing is less than a predetermined value.

  If an affirmative determination is made in step S104, the ECU 8 once ends the execution of this routine. On the other hand, if a negative determination is made in step S104, the ECU 8 proceeds to step S105.

  In step S105, it is determined whether or not the estimated ignition timing is advanced with respect to the target ignition timing. If a positive determination is made in step S105, the process proceeds to step S106. On the other hand, if a negative determination is made in step S105, the process proceeds to step S107.

  In step S106, the internal EGR gas amount is corrected to decrease, and the external EGR gas amount is corrected to increase so as to offset the decrease in the in-cylinder oxygen concentration caused by the internal EGR gas amount decrease correction. Specifically, the variable valve mechanism 9 is operated so as to shorten the negative valve overlap period of the intake valve 23 and the exhaust valve 33, and the opening degree of the EGR valve 42 is operated in the valve opening direction. As a result, the in-cylinder temperature decreases and the ignition timing is corrected to the retard side.

  In step S107, the internal EGR gas amount is corrected to increase, and the external EGR gas amount is corrected to decrease so as to offset the increase in the in-cylinder oxygen concentration caused by the increase correction of the internal EGR gas amount. Specifically, the variable valve mechanism 9 is operated so as to extend the negative valve overlap period of the intake valve 23 and the exhaust valve 33, and the opening degree of the EGR valve 42 is operated in the valve closing direction. As a result, the in-cylinder temperature rises and the ignition timing is corrected to the advance side.

  After executing step S106 or step S107, the ECU 8 once ends the execution of this routine. In the case of the present embodiment, the ECU 8 that executes Step S106 and Step S107 corresponds to the correcting means of the present invention.

  By executing the above routine, it is possible to control the fuel ignition timing to the target ignition timing while suppressing deterioration of the combustion characteristics depending on the in-cylinder oxygen concentration.

  The above-described embodiment is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, in the above embodiment, the ignition timing is controlled by feedback control based on the comparison between the estimated ignition timing and the target ignition timing, but the actual ignition timing is measured and the measurement result is compared with the target ignition timing. The ignition timing may be controlled based on the above. As a method of measuring the actual ignition timing, for example, a method of providing a sensor for detecting the in-cylinder pressure and detecting the actual ignition timing based on the detection value of the sensor can be exemplified. In this case, only the process executed in step S103 of the flowchart is changed to “measurement of the actual ignition timing by the in-cylinder pressure detection sensor”, and other processes can be executed in the same manner as in the above embodiment.

  Also, in the configuration in which the actual ignition timing is predicted by estimation calculation as in the above embodiment, a device for detecting the ignition timing such as the in-cylinder pressure detection sensor is attached, and the actually measured ignition timing is used for the calculation processing of the estimated ignition timing. Feedback may be provided. By doing so, for example, the deviation between the actual ignition timing and the estimated ignition timing when the cetane number of the fuel changes greatly can be corrected. Since it is not necessary to always perform this correction, the control accuracy of the ignition timing can be further improved without impairing the merit that can be enjoyed by the configuration that predicts the actual ignition timing by the estimation calculation as described above.

It is a figure which shows schematic structure of the intake system and exhaust system of an internal combustion engine to which the ignition timing control apparatus of Example 1 of this invention is applied. It is a block diagram which shows the outline | summary of the ignition timing control of Example 1 of this invention. It is a flowchart which shows the routine which performs ignition timing control of Example 1 of this invention.

Explanation of symbols

1 Internal combustion engine 2 Combustion chamber 3 Piston 5 Cylinder 6 Fuel injection valve 7 Accelerator pedal 8 ECU
9 Variable Valve Mechanism 20 Intake Port 21 Intake Manifold 22 Intake Pipe 23 Intake Valve 30 Exhaust Port 31 Exhaust Manifold 32 Exhaust Pipe 33 Exhaust Valve 40 EGR Device 41 EGR Passage 42 EGR Valve 70 Water Temperature Sensor 71 Crank Position Sensor 72 Accelerator Opening Sensor 73 Intake air temperature sensor 75 Air flow meter

Claims (3)

EGR means for returning a part of the exhaust from the internal combustion engine to the cylinder of the internal combustion engine;
A target ignition timing determining means for determining a target ignition timing of the fuel according to an operating state of the internal combustion engine;
Ignition timing acquisition means for acquiring by estimating or detecting the actual ignition timing of the fuel;
Oxygen concentration acquisition means for acquiring by estimating or detecting in-cylinder oxygen concentration;
The exhaust gas returned to the cylinder by the EGR means so that the target ignition timing and the ignition timing acquired by the ignition timing acquisition means coincide with each other and the oxygen concentration acquired by the oxygen concentration acquisition means does not change. Correction means for correcting the amount;
An ignition timing control device for an internal combustion engine, comprising: In claim 1,
The EGR means includes
An external EGR means for recirculating a part of the exhaust to the cylinder via an EGR passage connecting the exhaust passage and the intake passage of the internal combustion engine;
Internal EGR means for leaving a portion of the burned gas in the cylinder;
Have
The correction means includes
Internal EGR correction means for correcting the amount of exhaust gas remaining in the cylinder by the internal EGR means so that the target ignition timing and the ignition timing acquired by the ignition timing acquisition means coincide with each other;
External EGR correction means for correcting the amount of exhaust gas recirculated by the external EGR means so as to cancel out a change in in-cylinder oxygen concentration caused by correction of the amount of exhaust gas remaining in the cylinder by the internal EGR correction means; ,
An ignition timing control device for an internal combustion engine, comprising: In claim 2,
The correction means includes
When the ignition timing acquired by the ignition timing acquisition means is advanced from the target ignition timing, the internal EGR means corrects the amount of exhaust gas remaining in the cylinder by reducing the amount, and the external EGR means Correct the increase in the amount of exhaust gas that recirculates,
When the ignition timing acquired by the ignition timing acquisition means is retarded from the target ignition timing, the internal EGR means corrects the amount of exhaust gas remaining in the cylinder by increasing, and the external EGR means An ignition timing control device for an internal combustion engine, wherein the amount of exhaust gas recirculating is corrected to decrease.

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