JP2015086715A - Intake air quantity control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intake air quantity control device for an internal combustion engine where EGR control is performed, capable of suppressing the occurrence of troubles due to a pressure drop in an intake passage.SOLUTION: In an internal combustion engine 1, exhaust gas recirculation control is performed to recirculate part of exhaust gas as EGR gas into an intake passage 4. A control device 8 controls the quantity of intake air through the opening adjustment of an intake air throttle valve 3 provided in the intake passage 4 of the internal combustion engine 1. When an EGR rate to be regulated by the exhaust gas recirculation control is not higher than a predetermined value, the control device 8 restricts the valve closure amount of the intake air throttle valve so that the concentration of unburnt HC in the exhaust gas is not higher than a predetermined concentration and a pressure in the intake passage 4 on the further downstream side of the intake air than the intake air throttle valve 3 is not lower than a predetermined pressure.

Description

  The present invention relates to an intake air amount control device that controls the amount of intake air taken into an internal combustion engine.

  The intake passage of the internal combustion engine is provided with an intake air metering valve that controls the amount of intake air through opening adjustment. Further, as described in, for example, Patent Document 1, an exhaust gas recirculation device (hereinafter referred to as an EGR device) that recirculates a part of the exhaust gas of the internal combustion engine to an intake passage is used as a device employed in an internal combustion engine such as a vehicle. is there. When the exhaust gas is recirculated by the EGR device, the combustion temperature of the internal combustion engine is lowered, so that the amount of NOx generated in the internal combustion engine can be reduced.

  In such exhaust gas recirculation control, the EGR amount that is the amount of EGR gas recirculated to the intake passage is metered through the opening control of the EGR control valve, whereby the EGR rate [EGR rate = EGR amount / (EGR amount). + New air amount)] is adjusted to a ratio according to the engine operating state.

JP-A-2-267360

  Here, when the EGR amount decreases and the EGR rate decreases, the EGR partial pressure in the intake air of the internal combustion engine decreases, so the pressure in the intake passage decreases. If the opening of the intake metering valve is excessively controlled to the closed side while the pressure in the intake passage is reduced in this way, the pressure in the intake passage further decreases. There is a risk of such inconvenience.

First, since the compression end temperature in the combustion chamber decreases and the ignition of the air-fuel mixture becomes unstable, the discharge amount (concentration) of unburned HC from the internal combustion engine tends to increase.
Also, in an internal combustion engine, the pressure in the cylinder is lower than in the crankcase, so the engine lubricating oil tends to flow into the cylinder from the joint of the piston ring, etc., so-called oil rise tends to occur, and oil consumption May increase.

  Also, in the intake stroke of the internal combustion engine, when the connecting rod is pulled down by rotation of the crankshaft in a state where the pressure in the cylinder is lower than in the crankcase, the space between the crankshaft and the connecting rod is satisfied. Cavitation occurs in the lubricating oil. There is a possibility that bubbles generated by the cavitation may burst when moving to the compression stroke, generating abnormal noise such as “cracking”, peeling of the bearing surface layer, or the like.

  The present invention has been made in view of such a situation, and an object of the present invention is to control an intake air amount control apparatus capable of suppressing the occurrence of inconvenience due to a pressure drop in an intake passage in an internal combustion engine in which EGR control is performed. Is to provide.

  An intake air amount control device for an internal combustion engine that solves the above problems is applied to an internal combustion engine that performs exhaust gas recirculation control in which a part of exhaust gas is recirculated to an intake passage as EGR gas, and is provided in the intake passage of the internal combustion engine. The amount of intake air is controlled by adjusting the opening of the intake metering valve. Then, when the EGR rate adjusted by the exhaust gas recirculation control is equal to or less than a predetermined value, the intake air amount control device has an unburned HC concentration in the exhaust gas that is not more than a specified concentration and is located downstream of the intake air metering valve. The valve closing amount of the intake metering valve is limited so that the condition that the pressure in the passage is equal to or higher than the specified pressure is satisfied.

  According to this configuration, when the EGR gas decreases and the EGR rate falls below a predetermined value, the closing amount of the intake metering valve is limited so as to satisfy the above condition. Therefore, the pressure in the intake passage on the downstream side of the intake air becomes excessively low by controlling the intake air metering valve to the closed side excessively while the EGR rate is reduced. Can be suppressed. As a result, it is possible to suppress the occurrence of inconveniences as described above, for example, an increase in the amount of unburned HC discharged, an increase in oil consumption, the occurrence of abnormal noise, damage to the bearings, and the like.

1 is a schematic diagram showing an intake / exhaust system of an internal combustion engine to which the intake air amount control device for an internal combustion engine of one embodiment is applied. The block diagram for setting the final throttle valve opening. The block diagram for calculating a closing side guard value. The graph which shows the correspondence of an EGR rate ratio and an interpolation factor. The graph which shows the correspondence of an EGR rate and a closing side guard value. The graph which shows the relationship between an EGR rate and HC density | concentration when the opening degree of an intake throttle valve is restrict | limited by the closing side guard value. The graph which shows the relationship between an EGR rate and the intake pressure when the opening degree of an intake throttle valve is restrict | limited by the close side guard value.

Hereinafter, an embodiment in which an intake air amount control device for an internal combustion engine is embodied will be described with reference to FIGS.
FIG. 1 shows an intake / exhaust system of a diesel engine (hereinafter referred to as an internal combustion engine) provided with an intake air amount control device in the present embodiment. As shown in FIG. 1, an intake passage 4 is connected to the internal combustion engine 1. A surge tank 2 is provided in the intake passage 4. An intake throttle valve 3 as an intake air adjustment valve for adjusting the intake air amount is provided in the intake passage 4 and upstream of the intake of the surge tank 2.

  An exhaust passage 6 is connected to the internal combustion engine 1, and a variable capacity turbocharger 13 that supercharges intake air using exhaust pressure is provided in the middle of the exhaust passage 6. In the turbocharger 13, a turbine vane 13b to which the exhaust passage 6 is connected is provided with a nozzle vane for adjusting the exhaust flow rate, and the opening degree of the nozzle vane is changed according to the engine operating state. For example, by reducing the opening of the nozzle vane in the low load region, even if the exhaust flow rate is small, the exhaust flow velocity is increased and the exhaust dynamic pressure is increased. Further, by increasing the opening degree of the nozzle vanes in the high load region, the pressure loss of the exhaust gas when the exhaust gas flow rate is large is reduced.

  In the turbocharger 13, an intercooler 14 is provided in the intake passage 4 between the compressor housing 13 a to which the intake passage 4 is connected and the intake throttle valve 3. The intercooler 14 cools the intake air whose temperature has risen due to supercharging of the turbocharger 13.

Further, in the middle of the exhaust passage 6, a catalyst 7 for purifying the exhaust is provided downstream of the turbine housing 13 b of the turbocharger 13.
On the other hand, the internal combustion engine 1 is provided with an exhaust gas recirculation device (hereinafter referred to as an EGR device) that recirculates a part of the exhaust gas to the intake passage 4 as EGR gas. The EGR device is provided with an EGR gas recirculation passage 10 which is provided in the exhaust passage 6 and is branched from the exhaust upstream of the turbine housing 13 b, and the EGR gas recirculation passage 10 is connected to the surge tank 2. Further, in the middle of the EGR gas recirculation passage 10, an EGR cooler 12 that exchanges heat between the EGR gas and the cooling water, an EGR control valve 11 that adjusts the amount of EGR gas flowing through the EGR gas recirculation passage 10, EGR A bypass passage 15 and the like that flow exhaust gas around the cooler 12 are disposed. The bypass passage 15 is provided with a bypass valve 16 for opening and closing the bypass passage 15.

  A part of the exhaust gas passing through the exhaust passage 6 is introduced into the EGR gas recirculation passage 10 as EGR gas, heat exchanged by the EGR cooler 12, and then recirculated to the intake passage 4 and again with the fresh air, the combustion chamber of the internal combustion engine 1 again. To be introduced. By performing such exhaust gas recirculation control to recirculate the EGR gas, the combustion temperature of the air-fuel mixture is lowered and the amount of NOx generated is reduced. When executing the exhaust gas recirculation control, the target EGR rate EP is set based on the engine operating state, for example, the fuel injection amount Q indicating the engine speed NE or the engine load of the internal combustion engine 1 (the target EGR rate EP is “0” or more and “1” or less). Then, the actual EGR rate [EGR rate = EGR amount / (EGR amount + fresh air amount)] is determined by the engine operation by adjusting the opening degree of the EGR control valve 11 to an opening degree corresponding to the target EGR rate EP. It is adjusted to a state suitable for the state.

  The engine operating state of the internal combustion engine 1 is detected by various sensors. For example, the crank angle sensor 60 detects the rotation angle of the crankshaft of the internal combustion engine 1, that is, the crank angle, and calculates the engine rotation speed NE based on the detection signal. The air flow meter 61 detects an intake air amount GA that is the amount of air taken into the internal combustion engine 1. The intake pressure sensor 62 detects the intake pressure PM in the surge tank 2. The intake air temperature sensor 63 detects the intake air temperature THA, which is the temperature of the intake air after passing through the intercooler 14. Further, the water temperature sensor 64 detects a water temperature THW that is the temperature of the cooling water of the internal combustion engine 1. The atmospheric pressure PA is detected by the atmospheric pressure sensor 65. Further, the accelerator operation amount ACCP, which is the amount of depression of the accelerator pedal, is detected by the accelerator sensor 67. Further, the throttle valve opening TA, which is the opening of the intake throttle valve 3, is detected by the intake throttle valve sensor 68.

  In the present embodiment, the state where the intake throttle valve 3 is fully opened is defined as the reference operation position of the intake throttle valve 3, and this fully open state is referred to as “throttle valve opening degree TA = 0%”. The fully closed state of the intake throttle valve 3 is “throttle valve opening degree TA = 100%”, and the opening degree of the intake throttle valve 3 is adjusted between 0% and 100%. Therefore, as the value of the throttle valve opening TA decreases, the intake throttle valve 3 operates on the open side, and the intake air amount GA increases.

  Various controls of the internal combustion engine 1 are performed by the control device 8. The control device 8 includes a CPU that executes arithmetic processing related to various controls, a ROM that stores programs and data necessary for the control, a RAM that temporarily stores the arithmetic results of the CPU, and signals between the outside and the outside. The input / output port for inputting / outputting is provided. The control device 8 controls the fuel injection control of the internal combustion engine 1, the opening degree control for adjusting the opening degree of the intake throttle valve 3 to the target opening degree, or the EGR control according to the engine operating state detected by various sensors. The exhaust gas recirculation control is performed through the opening degree control of the valve 11.

  By the way, in order to suppress the generation amount of NOx, it is desirable to increase the EGR amount as much as possible. Therefore, in this embodiment, a large amount of EGR gas is recirculated by controlling the opening degree of the intake throttle valve 3 as close as possible in a low load operation region or the like.

  Here, since the EGR partial pressure in the intake air of the internal combustion engine 1 decreases when the EGR amount is insufficient with respect to the original amount due to deposit accumulation or the like in the EGR gas recirculation passage 10, the intake air The intake pressure PM that is the pressure in the passage 4 is reduced.

Further, the decrease in the amount of EGR that causes a decrease in the intake pressure PM includes, for example, the following in addition to the deposit caused in the EGR gas recirculation passage 10.
When the air-fuel mixture burns, water vapor is generated. The water vapor becomes condensed water by being cooled by the EGR cooler 12 that cools the EGR gas. In order to prevent this condensed water from accumulating in the intake system, the amount of EGR is intentionally reduced according to engine operating conditions, the amount of fresh air is increased to increase the saturated water vapor pressure of the exhaust, and the generation of condensed water is suppressed. Sometimes. Also, if the air density decreases due to an increase in intake air temperature or a decrease in atmospheric pressure, the compression end temperature decreases. Therefore, in order to suppress such a decrease in compression end temperature, the EGR amount is intentionally decreased to reduce the amount of fresh air. May increase.

  When the intake pressure PM is reduced due to such a decrease in the EGR amount and the opening degree of the intake throttle valve 3 is excessively controlled to the closed side, the intake pressure PM further decreases. May cause inconvenience.

  First, since the compression end temperature in the combustion chamber decreases and the ignition of the air-fuel mixture becomes unstable, the discharge amount (concentration) of unburned HC from the internal combustion engine 1 tends to increase. When the discharge amount of unburned HC increases in this way, the unburned HC adheres to the EGR cooler 12 that cools the EGR gas, the nozzle vanes of the turbocharger 13, and the like, and deposits accumulate, and these EGR coolers 12 And there is a risk of deteriorating functions such as nozzle vanes. Further, when the light load operation of the internal combustion engine 1 is frequently used continuously, unburned HC accumulates in the exhaust system functional parts such as the catalyst 7 during the light load operation where the exhaust temperature is low. Thereafter, when performing a high load operation in which the exhaust temperature becomes high, the accumulated unburned HC is discharged from the exhaust passage 6 in a white smoke state before the catalyst 7 is activated.

  Further, in the internal combustion engine 1, since the pressure in the cylinder is lower than that in the crankcase, the so-called oil rise that the engine lubricating oil flows into the cylinder from the joint portion of the piston ring or the like easily occurs, and the oil consumption The amount may increase.

  Further, in the intake stroke of the internal combustion engine 1, when the connecting rod is pulled down by the rotation of the crankshaft when the pressure in the cylinder is lower than that in the crankcase, the space between the crankshaft and the connecting rod is filled. Cavitation occurs in the lubricant. The bubbles generated by the cavitation may burst at the time of transition to the compression stroke, and may generate an abnormal noise “cracking” or may cause peeling of the bearing surface layer.

  Therefore, in the present embodiment, when the EGR rate adjusted by the EGR control is equal to or lower than a predetermined value, the condition that the unburned HC concentration in the exhaust is equal to or lower than the specified concentration and the intake pressure PM is equal to or higher than the specified pressure is set. The valve closing amount of the intake throttle valve 3 is limited so as to satisfy the condition. Hereinafter, such restriction on the valve closing amount will be described.

  FIG. 2 is a block diagram for calculating the final throttle valve opening degree TAF that is the target opening degree of the intake throttle valve 3. The final throttle valve opening TAF is calculated by the control device 8 at predetermined intervals.

  As shown in FIG. 2, the base opening setting unit 100 determines the base opening TAB, which is the base value of the target opening of the intake throttle valve 3, based on the engine speed NE and the fuel injection amount Q of the internal combustion engine 1. Set. The base opening setting unit 100 includes a setting map optimized for EGR execution for recirculating EGR gas to the intake passage 4 and a setting map optimized for EGR cut that does not recirculate EGR gas. Each is prepared. During EGR execution, the base opening degree TAB that can obtain the amount of fresh air corresponding to the target EGR rate EP using the setting map for EGR execution is the engine rotation speed NE and the fuel of the internal combustion engine 1. It is set based on the injection amount Q. On the other hand, at the time of EGR cut, the base opening degree TAB is set based on the engine rotational speed NE and the fuel injection amount Q of the internal combustion engine 1 using the setting map for EGR cut.

In the present embodiment, the fuel injection amount Q is used as a value indicating the engine load. However, other values such as the accelerator operation amount ACCP may be used.
The atmospheric pressure correction coefficient setting unit 110 sets the atmospheric pressure correction coefficient K1 based on the atmospheric pressure PA.

The intake air temperature correction coefficient setting unit 120 sets the intake air temperature correction coefficient K2 based on the intake air temperature THA.
The water temperature correction coefficient setting unit 130 sets the water temperature correction coefficient K3 based on the water temperature THW.

  The environmental correction coefficient calculation unit 140 calculates a multiplication value of the atmospheric pressure correction coefficient K1, the intake air temperature correction coefficient K2, and the water temperature correction coefficient K3, and sets the calculated multiplication value as the environmental correction coefficient KE.

  The first throttle valve opening calculation unit 150 calculates a first throttle valve opening TAE that is a value obtained by multiplying the base opening TAB by the environment correction coefficient KE. By calculating the first throttle valve opening TAE, the base opening TAB of the intake throttle valve 3 is environmentally corrected according to the atmospheric pressure PA, the intake air temperature THA, and the water temperature THW.

  When the first throttle valve opening degree TAE is calculated in this way, the final throttle valve opening degree setting unit 160 sets the final throttle valve opening degree TAF that is the final target opening degree of the intake throttle valve 3. In the final throttle valve opening setting section 160, the smaller one of the above-mentioned closing side guard value TAG and first throttle valve opening TAE is set as the final throttle valve opening TAF. Therefore, when the first throttle valve opening degree TAE is smaller than the closing guard value TAG, that is, when the first throttle valve opening degree TAE is an opening degree that is more open than the closing guard value TAG, One throttle valve opening TAE is set to the final throttle valve opening TAF. On the other hand, when the first throttle valve opening TAE is larger than the closing guard value TAG, that is, when the first throttle valve opening TAE is closer to the closing side than the closing guard value TAG, the first throttle valve opening TAE is closed. By setting the side guard value TAG to the final throttle valve opening degree TF, the opening degree of the intake throttle valve 3 is limited so as not to be the opening degree on the closing side with respect to the closing side guard value TAG.

When the final throttle valve opening degree TAF is thus set, the opening degree of the intake throttle valve 3 is adjusted so that the throttle valve opening degree TA coincides with the final throttle valve opening degree TAF.
Next, a procedure for calculating the closing guard value TAG, which is a value that suppresses excessive closing of the intake throttle valve 3 and restricts the closing amount of the intake throttle valve 3, will be described.

FIG. 3 shows a block diagram for calculating the closing guard value TAG. The closing guard value TAG is also calculated by the control device 8 every predetermined period.
First, the correction start EGR rate setting unit 200 sets the correction start EGR rate EHS based on the engine speed NE and the fuel injection amount Q. The correction start EGR rate EHS determines whether either the target EGR rate EP or the estimated EGR rate ES is low enough to cause the occurrence of inconvenience due to the decrease in the intake pressure PM as described above. The value corresponding to the engine speed NE and the fuel injection amount Q is set in the map or the like by a preliminary experiment or the like. The correction start EGR rate EHS is a value not less than “0” and not more than “1”.

  Next, the target EGR rate reading unit 210 reads the currently set target EGR rate EP, and the estimated EGR rate reading unit 220 reads the currently calculated estimated EGR rate ES. The estimated EGR rate ES is an estimated value of the current EGR rate, and is calculated based on the intake air temperature THA, the intake pressure PM, the intake air amount GA, and the like. Further, the estimated EGR rate ES is a value of “0” or more and “1” or less.

  The EGR rate ratio calculation unit 230 refers to the target EGR rate EP read by the target EGR rate reading unit 210 and the estimated EGR rate ES read by the estimated EGR rate reading unit 220, from the following equation (1): The EGR rate ratio ERP is calculated. The EGR rate ratio ERP is a value not less than “0” and not more than “1”. When the value on the right side of the following equation (1) exceeds “1”, the EGR rate ratio ERP is “1”. Set to

ERP = min (EP, ES) / EHS (1)
ERP: EGR ratio
EP: Target EGR rate
ES: Estimated EGR rate EHS: Correction start EGR rate

As can be seen from Equation (1), the smaller one of the target EGR rate EP and the estimated EGR rate ES is selected, and the selected value is divided by the correction start EGR rate EHS. Accordingly, when any selected value of the target EGR rate EP and the estimated EGR rate ES exceeds the correction start EGR rate EHS or is the same, the EGR rate ratio ERP becomes “1”.

  On the other hand, when any selected value of the target EGR rate EP and the estimated EGR rate ES is lower than the correction start EGR rate EHS, the EGR rate ratio ERP becomes a value smaller than “1”. Further, when the selected value of either the target EGR rate EP or the estimated EGR rate ES is below the correction start EGR rate EHS, the opening degree of the intake throttle valve 3 is suitable for EGR execution. The opening is gradually changed from the opening to the opening suitable for EGR cut.

When the EGR rate ratio ERP is calculated by the EGR rate ratio calculation unit 230, the interpolation coefficient setting unit 240 sets the interpolation coefficient K4 based on the EGR rate ratio ERP.
As shown in FIG. 4, the interpolation coefficient K4 is a value between “0” and “1” and has a linear linear relationship with the EGR rate ratio ERP. That is, the EGR rate ratio ERP is set to the value of the interpolation coefficient K4 as it is. For example, when the EGR rate ratio ERP is “0”, the interpolation coefficient K4 is set to “0”, and the EGR rate ratio When the ERP is “1”, the interpolation coefficient K4 is set to “1”, and when the EGR rate ratio ERP is “0.5”, the interpolation coefficient K4 is set to “0.5”. The correspondence relationship between the EGR rate ratio ERP and the interpolation coefficient K4 is merely an example. For example, as shown by a two-dot chain line in FIG. 4, the EGR rate ratio ERP and the interpolation coefficient have a curved linear relationship. A correspondence relationship with K4 may be set.

  When the interpolation coefficient K4 is set in this way, the final interpolation coefficient setting unit 260 sets the smaller one of the interpolated coefficient K4K after the gradual change and the interpolation coefficient K4 set by the interpolation coefficient setting unit 240 as the final interpolation coefficient K4F. Set. The post-gradual change interpolation coefficient K4K is a value calculated by the interpolation coefficient gradual change unit 250. In this interpolation coefficient gradual change unit 250, a value obtained by adding a predetermined gradual change amount to the previous value of the final interpolation coefficient K4F. Is set as the interpolation coefficient K4K after gradual change. By such setting of the final interpolation coefficient K4F, even if the interpolation coefficient K4 set by the interpolation coefficient setting unit 240 changes suddenly, a sudden change in the final interpolation coefficient K4F can be suppressed.

  Next, the EGR cut closing guard value setting unit 270 sets the EGR cutting closing guard value TACG based on the engine speed NE and the fuel injection amount Q. The closing side guard value TACG at the time of EGR cut is such that the HC concentration in the exhaust gas is equal to or less than a predetermined restriction HC concentration HCL and the intake pressure PM is a predetermined restriction at the time of EGR cut in which the EGR gas is not recirculated to the exhaust passage 6. This is the maximum opening to the closing side of the intake throttle valve 3 that can satisfy the condition that the intake pressure is PML or higher. If the opening of the intake throttle valve 3 is closer to the closing side than the closing side guard value TACG during EGR cut, the above-described inconvenience is likely to occur due to an excessive decrease in the intake pressure PM. Note that the correspondence relationship between the engine speed NE and the fuel injection amount Q and the EGR cut closing guard value TACG is obtained through experiments or the like in advance.

  Further, the EGR execution closing side guard value setting unit 280 sets the EGR execution closing side guard value TAEG based on the engine speed NE and the fuel injection amount Q. The closing side guard value TAEG at the time of EGR execution is such that the HC concentration in the exhaust gas is equal to or less than a predetermined restriction HC concentration HCL and the intake pressure PM is a predetermined restriction at the time of EGR execution for recirculating EGR gas to the exhaust passage 6. This is the maximum opening to the closing side of the intake throttle valve 3 that can satisfy the condition that the intake pressure is PML or higher. If the intake throttle valve 3 has an opening closer to the closing side than the closing side guard value TAEG at the time of EGR execution, the above-described inconvenience is likely to occur due to an excessive decrease in the intake pressure PM. It should be noted that the correspondence relationship between the engine speed NE and the fuel injection amount Q and the EGR execution side closing side guard value TAEG is also obtained through experiments and the like in advance. Note that, at the same engine speed NE and the same fuel injection amount Q, the value of the closing guard value TAEG at the time of EGR execution is larger than the value of the closing guard value TACG at the time of EGR cut, that is, the closing side guard value TACG. Set to a value.

Next, the closing guard value calculation unit 290 calculates a final closing guard value TAG from the following equation (2).

TAG = TACG− (TACG−TAEG) × K4F (2)
TAG: Close side guard value TACG: Close side guard value at EGR cut TAEG: Close side guard value at EGR execution
K4F: Final interpolation coefficient

As can be seen from the above equation (2), the closing guard value TAG is calculated as an interpolated value between the EGR cut closing guard value TACG and the EGR execution closing guard value TAEG.

Then, the final throttle valve opening setting unit 160 shown in FIG. 1 uses the calculated closing guard value TAG to limit the opening of the intake throttle valve 3 to the closing side.
Next, the effect | action of this embodiment is demonstrated, referring FIGS. FIG. 5 shows an example of the transition of the closed-side guard value TAG when the estimated EGR rate ES is selected in the “min (EP, ES)” section of the above formula (1). Even when the target EGR rate EP is selected in the “min (EP, ES)” item of (1), the closing side guard value TAG changes in the same manner. However, a certain amount of response delay exists between the time when the opening degree of the EGR control valve 11 changes and the time when the actual EGR rate changes. Therefore, when the target EGR rate EP that is the control target value of the EGR control valve 11 is selected in the term “min (EP, ES)” of the above equation (1), the estimated EGR indicating the actual EGR rate is selected. The closing side guard value TAG is calculated at an earlier time than when the rate ES is selected. Therefore, for example, before the intake pressure PM is excessively decreased due to a decrease in the actual EGR rate, it is possible to limit the opening of the intake throttle valve 3 to the closing side.

  On the other hand, when the estimated EGR rate ES indicating the actual EGR rate is selected in the term “min (EP, ES)” of the above formula (1), deposits and the like in the EGR gas recirculation passage 10 Thus, in the case where the actual EGR amount is insufficient with respect to the original EGR amount corresponding to the target EGR rate, it is possible to limit the opening of the intake throttle valve 3 to the closing side.

  When the estimated EGR rate ES (or the target EGR rate EP) falls below the correction start EGR rate EHS described above, the opening degree of the intake throttle valve 3 is suitable from the opening degree suitable for EGR execution to that suitable for EGR cut as described above. It gradually changes toward the opening. Further, when the estimated EGR rate ES (or the target EGR rate EP) falls below the correction start EGR rate EHS described above, the EGR rate ratio ERP becomes a value smaller than “1”, and unless there is a sudden change in the interpolation coefficient K4, etc. The final interpolation coefficient K4F is set to the same value as the EGR rate ratio ERP. As the estimated EGR rate ES is smaller, the value of the numerator is smaller than the denominator of the above formula (1), so the EGR rate ratio ERP is smaller and the final interpolation coefficient K4F is also smaller. When the final interpolation coefficient K4F is reduced in this way, as can be seen from the above equation (2), the closing guard value TAG approaches the closing guard value TACG at the time of EGR cut, so the closing side of the intake throttle valve 3 is closed. The limit value (= closed guard value TAG) changes in the direction in which the intake throttle valve 3 opens more.

  That is, as shown in FIG. 5, the closer the estimated EGR rate ES is, the smaller the closed guard value TAG is. Therefore, as the EGR partial pressure is lower, the opening degree of the intake throttle valve 3 when the closing side opening degree of the intake throttle valve 3 is limited by the closing side guard value TAG becomes the open side, and the intake air amount increases. Become. Accordingly, as the amount of decrease in the intake pressure PM increases due to the decrease in the EGR amount, the minimum intake air amount increases, so that an excessive decrease in the intake pressure PM can be suppressed.

  Further, as described above, the EGR cut closing guard value TACG and the EGR execution closing guard value TAEG used in the above equation (2) both have an HC concentration in the exhaust gas that is equal to or less than a prescribed restricted HC concentration HCL. Further, the opening degree of the intake throttle valve 3 is set so as to satisfy the condition that the intake pressure PM is equal to or higher than a prescribed restricted intake pressure PML. Therefore, when the opening degree of the intake throttle valve 3 is limited by the closing guard value TAG which is a value interpolating between the EGR cut closing guard value TACG and the EGR execution closing guard value TAEG, As shown in FIG. 6, even if the estimated EGR rate ES (or the target EGR rate EP) changes, the HC concentration (line L1) is maintained below the restricted HN concentration HCL. When the opening degree of the intake throttle valve 3 is limited by the closing side guard value TAG, as shown in FIG. 7, even if the estimated EGR rate ES (or the target EGR rate EP) changes, the intake pressure PM (line L2) is maintained at or above the restricted intake pressure PML.

As described above, according to the present embodiment, the following effects can be obtained.
(1) When the EGR gas decreases and either the estimated EGR rate ES or the target EGR rate EP falls below the correction start EGR rate EHS, the unburned HC concentration in the exhaust gas is below the restricted HC concentration HCL and The valve closing amount of the intake throttle valve 3 is limited by the closing guard value TAG so as to satisfy the condition that the atmospheric pressure PM becomes equal to or higher than the restricted intake pressure PML. Therefore, the pressure in the intake passage 4 on the intake downstream side of the intake throttle valve 3 is controlled by excessively controlling the intake throttle valve 3 to the closed side while the estimated EGR rate ES and the target EGR rate EP are decreasing. Can be suppressed from becoming excessively low. As a result, it is possible to suppress the occurrence of inconveniences such as those described above, for example, an increase in the amount of unburned HC discharged, an increase in oil consumption, the occurrence of abnormal noise, and damage to the bearing.

In addition, the said embodiment can also be changed and implemented as follows.
In the EGR rate ratio calculation unit 230, the smaller one of the target EGR rate EP and the estimated EGR rate ES is selected. In addition, such selection processing may be omitted, and the EGR rate ratio ERP may be calculated based on the estimated EGR rate ES, or may be calculated based on the target EGR rate EP.

  When the EGR rate ratio ERP calculated by the above equation (1) is a value smaller than “1”, one of the target EGR rate EP and the estimated EGR rate ES is selected as the correction start EGR rate. Judging that it is below EHS. In addition, the target EGR rate EP and the estimated EGR rate ES may be directly compared with the correction start EGR rate EHS to determine whether the target EGR rate EP and the estimated EGR rate ES are below the correction start EGR rate EHS. Good. When it is determined that the target EGR rate EP or the estimated EGR rate ES is lower than the correction start EGR rate EHS, the target EGR rate EP or the estimated EGR rate ES and the correction start EGR rate EHS depend on the degree of divergence. Thus, the interpolation coefficient K4 may be set.

The calculation of the closing side guard value TAG by the above equation (2) is an example, and the closing side guard value TAG may be calculated in another manner.
The closed side guard value TAG may be calculated from the above equation (2) using the interpolation coefficient K4 set by the interpolation coefficient setting unit 240, omitting the interpolation coefficient gradual change unit 250 and the final interpolation coefficient setting unit 260. .

  -Although the internal combustion engine of the said embodiment was a diesel engine, it can implement similarly with a gasoline engine. In general, in a gasoline engine, the reference operation position is often set to a state in which an intake metering valve (for example, a throttle valve) is fully closed. Accordingly, in the case of a gasoline engine, for example, the fully closed state of the intake metering valve is “opening of the intake metering valve = 0%”, and the fully open state of the intake metering valve is “opening of the intake metering valve = 100% ". In this case, as the opening of the intake metering valve increases, the intake metering valve operates to open, and the intake air amount GA increases. In other words, in the case of the diesel engine described above, the intake air amount GA increases as the opening value (0% to 100%) of the intake air adjustment valve decreases. As the value of the amount valve opening (0% to 100%) increases, the intake air amount GA increases. In this way, in the case of a gasoline engine, if the closing side guard value TAG is set in consideration of the point that the value of the opening of the intake metering valve and the change direction of the intake air amount are reversed. In addition, it is possible to suppress the occurrence of inconvenience due to excessive reduction of the intake pressure PM, for example, increase in oil consumption, generation of abnormal noise, damage to the bearing, and the like.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Surge tank, 3 ... Intake throttle valve, 4 ... Intake passage, 6 ... Exhaust passage, 7 ... Catalyst, 8 ... Electronic control unit, 10 ... EGR gas recirculation passage, 11 ... EGR control valve, 12 DESCRIPTION OF SYMBOLS ... EGR cooler, 13 ... Turbocharger, 13a ... Compressor housing, 13b ... Turbine housing, 14 ... Intercooler, 15 ... Bypass passage, 16 ... Bypass valve, 60 ... Crank angle sensor, 61 ... Air flow meter, 62 ... Intake pressure sensor , 63 ... intake air temperature sensor, 64 ... water temperature sensor, 65 ... atmospheric pressure sensor, 67 ... accelerator sensor, 68 ... intake throttle valve sensor, 100 ... base opening setting unit, 110 ... atmospheric pressure correction coefficient setting unit, 120 ... air temperature correction Coefficient setting unit, 130 ... Water temperature correction coefficient setting unit, 140 ... Environment correction coefficient calculation unit, 150 ... First throttle valve opening calculation unit, 160 ... Final throttle Valve opening setting unit, 200 ... correction start EGR rate setting unit, 210 ... target EGR rate reading unit, 220 ... estimated EGR rate reading unit, 230 ... EGR rate ratio calculation unit, 240 ... interpolation coefficient setting unit, 250 ... interpolation coefficient Gradual change unit, 260... Final interpolation coefficient setting unit, 270... EGR cut closing side guard value setting unit, 280... EGR execution closing side guard value setting unit, 290.

Claims (1)

Applied to an internal combustion engine in which exhaust gas recirculation control is performed to recirculate part of the exhaust gas as EGR gas to the intake passage, and the amount of intake air is controlled by adjusting the opening of an intake air metering valve provided in the intake passage of the internal combustion engine An intake air amount control device,
When the EGR rate adjusted by the exhaust gas recirculation control is equal to or less than a predetermined value, the unburned HC concentration in the exhaust gas is equal to or lower than the predetermined concentration, and the pressure in the intake passage on the intake downstream side of the intake metering valve is predetermined. An intake air amount control device for an internal combustion engine, wherein the valve closing amount of the intake air metering valve is limited so as to be equal to or higher than the pressure.