JP4057984B2 - Fuel injection control device for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection control device for an internal combustion engine that controls an injection pressure of fuel to be used for combustion, and more particularly to an improvement in a control structure for suppressing deterioration of combustion noise.

  As an apparatus applied to an internal combustion engine, an exhaust gas recirculation (EGR) apparatus that recirculates part of exhaust gas into intake air is known. In an internal combustion engine equipped with such an EGR device, the EGR amount is adjusted according to the engine operating state through opening control of an EGR valve provided in the EGR path.

  Now, when a sudden introduction of EGR gas is required due to changes in the engine operating state, the EGR valve is opened rapidly. However, due to the delay in the flow of EGR gas in the EGR path, the amount of EGR is actually increased. It takes a certain amount of time for the increase to occur. In the meantime, the control amount of the fuel injection system, such as the injection amount and the injection timing, has already been changed to a value premised on the introduction of the EGR gas in accordance with the change in the operation state during the period. For this reason, immediately after the rapid introduction of EGR as described above, combustion is temporarily activated more than expected, and combustion noise may be deteriorated.

  Therefore, conventionally, as seen in, for example, Patent Document 1, a fuel injection control device for an internal combustion engine that temporarily reduces the fuel injection pressure immediately after the rapid introduction of EGR has been proposed. Such a reduction in injection pressure acts to inactivate combustion by suppressing atomization of the injected fuel. Therefore, activation of combustion during the response delay period of the intake system is suppressed, and combustion noise is deteriorated. Will be suppressed.

If the injection pressure is immediately returned to the original value immediately after the response delay period of the intake system, a torque shock occurs due to a sudden change in the injection pressure. Therefore, in the conventional fuel injection control device, after the injection pressure is reduced, the injection pressure is gradually changed to the increased pressure side to return to the original value.
Japanese Patent Application Laid-Open No. 2002-235587

  By the way, the deterioration of the combustion noise may occur not only in the control transition period accompanied by the response delay of the intake system such as after the resumption of EGR as described above. For example, during the EGR cut, there is no introduction of EGR gas that slows down the combustion, so it can be said that the combustion noise is likely to deteriorate not only immediately after the restart but also throughout.

  Further, in recent years, in a lean combustion internal combustion engine such as a diesel engine, an internal combustion engine that operates while switching a combustion mode between low-temperature combustion and normal combustion that simultaneously reduce smoke emissions and NOx emissions by introducing a large amount of EGR has been introduced. Proposed. At the time of normal combustion in such an internal combustion engine, the combustion is likely to be activated and the combustion noise is likely to be deteriorated as compared to low temperature combustion where the combustion becomes slow due to the introduction of a large amount of EGR. Accordingly, there is a demand not only for the control transition period as described above, but also for suppressing the deterioration of combustion noise in a wide area.

  Further, in the above conventional technique, when returning the injection pressure that has been reduced to suppress the deterioration of the combustion noise to the original value, the rate of change of the injection pressure to the pressure increase side is gradually changed. In order to resume normal control at an early stage, it is desirable to quickly return the injection pressure. However, in the above conventional technology, through such gradual change, when the injection pressure is restored after the deterioration of the combustion noise is suppressed, the injection pressure is suddenly changed to prevent the occurrence of torque shock. For that purpose, such a return delay is inevitable.

  A problem to be solved by the present invention is a fuel injection control device for an internal combustion engine that can achieve early recovery from suppression control of deterioration of combustion noise while suitably suppressing deterioration of combustion noise other than the control transition period. It is to provide.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
The invention according to claim 1 is applied to an internal combustion engine including an exhaust gas recirculation valve that adjusts an exhaust gas recirculation amount into intake air, and controls the injection pressure of fuel supplied to combustion. In the device, when the predetermined condition including the upper limit condition of the opening degree of the exhaust gas recirculation valve is established, it is determined that the operating condition is likely to deteriorate the combustion noise, and when it is determined that the operating condition is present, And a gradual change of the injection pressure at a first rate of change when the injection pressure is changed to a reduced pressure side at the start of the reduction of the injection pressure by the reduction means. In addition, when the predetermined condition is not satisfied when the injection pressure is changed to the pressure increase side at the end of the reduction of the injection pressure by the reduction means, the predetermined period is smaller than the first change rate. Of is gradual change in pressure increasing the injection pressure at a changing rate, that then with the gradual change means for gradually changing the injection pressure at its larger than the second change rate third change rate, the The gist.

  According to a second aspect of the present invention, in the fuel injection control device for an internal combustion engine according to the first aspect, the upper limit opening degree in the upper limit condition of the opening degree of the exhaust gas recirculation valve is set to a fully closed / open state of the exhaust gas recirculation valve. The gist is the degree.

  The invention according to claim 3 is the fuel injection control device of the internal combustion engine according to claim 1 or 2, wherein the internal combustion engine operates while switching the combustion mode between a plurality of combustion modes. The gist is that the predetermined condition includes being in operation in a specific combustion mode in which the combustion state is more easily activated than the other combustion modes among the plurality of combustion modes.

  According to a fourth aspect of the present invention, in the fuel injection control device for an internal combustion engine according to any one of the first to third aspects, the predetermined condition includes a lower limit condition of atmospheric pressure. To do.

  According to a fifth aspect of the present invention, in the fuel injection control device for an internal combustion engine according to any one of the first to fourth aspects, as a calculation map of injection pressure based on engine operating conditions, a first calculation map; And a second calculation map set so that the map value of the injection pressure under the same engine operating condition is smaller than that of the first calculation map, and the calculation map used for calculation of the injection pressure is the first calculation map. The gist is to reduce the injection pressure by the reducing means by switching from one calculation map to the second calculation map.

  In the above configuration, when an upper limit condition of the exhaust gas recirculation (EGR) valve opening, that is, a predetermined condition including that the EGR valve opening is equal to or less than a predetermined value is satisfied, it is determined that the operating condition is likely to deteriorate combustion. Is made. In an operating situation where the EGR valve opening is small and the amount of EGR is small, the ratio of fresh air in the combustion chamber is high and combustion is likely to be activated, so that the combustion noise is likely to deteriorate. In particular, as described in claim 2, if the upper limit opening degree of the upper limit condition is the fully closed opening degree of the EGR valve, the EGR amount becomes zero when the predetermined condition is satisfied. Become.

  Now, in the above configuration, when the operating condition is likely to cause the deterioration of the combustion noise, the injection pressure is reduced and the atomization of the injected fuel is suppressed. Is suppressed, and the deterioration of combustion noise is suitably suppressed. In the above configuration, since the injection pressure is gradually changed when the injection pressure reduction starts and ends when the injection pressure is relatively large, the stability of the injection pressure control system can be suitably maintained.

  In the above configuration, since the upper limit condition of the EGR valve opening is included as one of the conditions for implementing the combustion noise reduction control by reducing the injection pressure, the EGR valve opening is rapidly opened due to a sudden increase in the EGR amount or the like. The reduction of the injection pressure is stopped, and the injection pressure is restored to the original value. At this time, due to a delay in the flow of EGR gas in the EGR path or the like, a certain amount of time is required for an increase in the actually introduced EGR amount for a while after the rapid increase in the EGR valve opening degree. In that respect, in the above configuration, since the injection pressure gradually changes to the pressure increase side at a relatively gradual second change rate from the end of the injection pressure reduction according to the failure of the predetermined condition, The injection pressure is maintained at a relatively low value during the delay period of the EGR amount increase, and the deterioration of the combustion noise during the delay period can be suitably suppressed. Further, in the above configuration, after the predetermined period has elapsed since the end of the injection pressure reduction, the injection pressure is gradually changed to the pressure increasing side at a relatively rapid third change rate, so that deterioration of combustion noise is suppressed. The injection pressure reduced as much as possible can be restored to its original value relatively quickly. Therefore, in the above configuration, it is possible to achieve early recovery from the suppression control of the combustion noise deterioration while suitably suppressing the deterioration of the combustion noise other than the control transition period.

  Note that in an internal combustion engine that operates while switching the combustion mode among a plurality of combustion modes, the control state of the injection system, intake system, etc. differs depending on the combustion mode being operated. The degree of activity may vary greatly depending on the combustion mode. And when it is in the combustion mode in which combustion is difficult to be activated, even if the EGR amount is reduced or the introduction of EGR is stopped, the combustion noise as described above is hardly deteriorated, or depending on the combustion mode, In the first place, there may be cases where the driving situation does not cause the combustion noise to deteriorate. In that respect, in the configuration according to claim 3, it is said that the injection is performed in a specific combustion mode in which the combustion state is more easily activated than the other combustion modes among the plurality of combustion modes. It is set as one of the implementation conditions of combustion noise reduction control by pressure reduction. Therefore, unnecessary injection pressure reduction when the operation is performed in the combustion mode in which the combustion noise is hardly deteriorated or is not deteriorated in the first place is suppressed, and the combustion noise can be more efficiently reduced. it can.

  When an internal combustion engine is operated at a low atmospheric pressure such as at high altitudes, combustion tends to become unstable due to a reduction in the amount of intake air. There is a risk of causing problems. In that respect, in the configuration according to claim 4, as one of the execution conditions for reducing the injection pressure, the lower limit condition of the atmospheric pressure is included, that is, the atmospheric pressure is not less than a predetermined value. Can be suitably avoided.

  In addition, the reduction of the injection pressure related to the suppression of the deterioration of the combustion noise can be easily and accurately performed by switching the calculation map for calculating the injection pressure as described in claim 5.

Hereinafter, an embodiment embodying the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a configuration of an internal combustion engine 10 to which the present embodiment is applied. The internal combustion engine 10 is a diesel engine including a common rail fuel injection device and a turbocharger 11, and mainly includes an intake passage 12, a combustion chamber 13, and an exhaust passage 14.

  In an intake passage 12 constituting the intake system of the internal combustion engine 10, an air flow meter 16, a compressor 17 of the turbocharger 11, an intercooler 18, And an intake throttle valve 19 is provided. The intake passage 12 is branched at an intake manifold 20 provided on the downstream side of the intake throttle valve 19 and connected to the combustion chamber 13 of each cylinder of the internal combustion engine 10 via an intake port 21.

  On the other hand, in the exhaust passage 14 constituting the exhaust system of the internal combustion engine 10, the exhaust port 22 connected to the combustion chamber 13 of each cylinder is connected to the exhaust turbine 24 of the turbocharger 11 via the exhaust manifold 23. Yes. In addition, a NOx catalytic converter 25, a PM filter 26, and an oxidation catalytic converter 27 are disposed downstream from the exhaust turbine 24 in the exhaust passage 14 in order from the upstream side.

  The NOx catalytic converter 25 carries an NOx storage reduction catalyst. The NOx catalyst stores NOx in the exhaust when the oxygen concentration of the exhaust is high, and releases the stored NOx when the oxygen concentration of the exhaust is low. Further, the NOx catalyst reduces and purifies the released NOx if there is sufficient unburned fuel component as a reducing agent at the time of releasing the NOx.

  The PM filter 26 that is an exhaust filter for collecting PM in the exhaust is formed of a porous material. Similar to the NOx catalytic converter 25, the PM filter 26 carries an NOx storage reduction catalyst, and purifies NOx in the exhaust gas. Further, the trapped PM is oxidized and removed by a reaction triggered by the NOx catalyst.

The oxidation catalyst converter 27 carries an oxidation catalyst, and HC and CO in the exhaust are oxidized and purified.
In addition, on the upstream side and the downstream side of the PM filter 26 in the exhaust passage 14, an inlet gas temperature sensor 28 that detects the inlet gas temperature that is the temperature of the exhaust gas flowing into the PM filter 26, and the exhaust gas after passing through the PM filter 26. An outgas temperature sensor 29 for detecting an outgas temperature, which is a temperature, is provided. The exhaust passage 14 is provided with a differential pressure sensor 30 for detecting a differential pressure between the exhaust upstream side of the PM filter 26 and the exhaust downstream side thereof. Further, two oxygen sensors 31 and 32 for detecting the oxygen concentration in the exhaust gas are arranged on the exhaust gas upstream side of the NOx catalytic converter 25 in the exhaust passage 14 and between the PM filter 26 and the oxidation catalytic converter 27, respectively. It is installed.

  Further, the internal combustion engine 10 is provided with an exhaust gas recirculation (hereinafter referred to as EGR) device that recirculates a part of the exhaust gas to the air in the intake passage 12. The EGR device includes an EGR passage 33 that allows the exhaust passage 14 and the intake passage 12 to communicate with each other. The most upstream portion of the EGR passage 33 is connected to the exhaust upstream side of the exhaust turbine 24 in the exhaust passage 14. The EGR passage 33 is provided with an EGR catalyst 34 for reforming the recirculated exhaust, an EGR cooler 35 for cooling the exhaust, and an EGR valve 36 for adjusting the flow rate of the exhaust from the upstream side. The most downstream portion of the EGR passage 33 is connected to the downstream side of the intake throttle valve 19 in the intake passage 12.

  On the other hand, an injector 40 for injecting fuel to be used for combustion in the combustion chamber 13 is disposed in the combustion chamber 13 of each cylinder of the internal combustion engine 10. The injector 40 of each cylinder is connected to a common rail 42 via a high pressure fuel supply pipe 41.

  High pressure fuel is supplied to the common rail 42 through a fuel pump 43. The pressure of the high pressure fuel in the common rail 42, that is, the rail pressure is detected by a rail pressure sensor 44 attached to the common rail 42. A relief valve 47 is attached to the common rail 42. The relief valve 47 is opened when the rail pressure becomes higher than a desired pressure, and a part of the high-pressure fuel in the common rail 42 is returned to the fuel tank to reduce the rail pressure.

  Further, a low pressure fuel having a pressure lower than that of the high pressure fuel sent to the common rail 42 is sent from the fuel pump 43. This low pressure fuel is supplied to the addition valve 46 through the low pressure fuel supply pipe 45.

  The electronic control unit 50 that controls various controls of the internal combustion engine 10 includes a CPU that executes various calculation processes related to the control of the internal combustion engine 10, a ROM that stores programs and data necessary for the control, a calculation result of the CPU, and the like. A RAM that is temporarily stored, an input / output port for inputting / outputting signals to / from the outside, and the like are provided. In addition to the sensors described above, the input port of the electronic control unit 50 includes an NE sensor 51 that detects the engine speed, an accelerator sensor 52 that detects the accelerator operation amount, and a throttle valve sensor that detects the opening of the intake throttle valve 19. 53, an atmospheric pressure sensor 54 for detecting the atmospheric pressure is connected. The output ports of the electronic control unit 50 are connected to drive circuits such as the intake throttle valve 19, the EGR valve 36, the fuel pump 43, and the relief valve 47.

  The electronic control unit 50 outputs a command signal to the drive circuit of each device connected to the output port according to the engine operating state grasped from the detection signal input from each sensor. Thus, fuel injection amount from the injector 40, control of fuel injection timing, fuel addition control from the addition valve 46, EGR control based on the opening control of the EGR valve 36 and the intake throttle valve 19, and from the addition valve 46 Various controls such as fuel addition control are performed by the electronic control unit 50.

  In the internal combustion engine 10, the EGR control is performed by feedback control of the opening degrees of the EGR valve 36 and the intake throttle valve 19 based on the oxygen concentration in the exhaust gas detected by the oxygen sensors 31 and 32. In this feedback control, first, based on the detection result of the oxygen concentration, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 13 is obtained, and the current EGR rate (EGR gas amount and intake air amount is calculated from the air-fuel ratio. Ratio) is calculated. The target opening (target EGR valve opening, target throttle valve opening) of the EGR valve 36 and the intake throttle valve 19 is set so that the EGR gas amount and the intake air amount at which the EGR rate becomes the target EGR rate can be obtained. The calculated opening is adjusted according to the target opening.

  The internal combustion engine 10 is operated while switching the combustion mode in accordance with the engine operating conditions such as the engine speed, the engine load, and the catalyst control request. The combustion modes that can be switched include the following four combustion modes.

<Normal combustion mode>
In the normal combustion mode, the EGR rate is set lower than the EGR rate at which the smoke emission amount reaches the peak, and combustion is performed at a lean air-fuel ratio. In the normal combustion mode, pilot injection, which is sub-injection prior to the main injection, is performed outside of the high rotational speed and high load range.

<Temperature increase multi-injection mode>
The temperature increase multi-injection mode is an after-injection that is sub-injection performed in the pilot injection and main injection, and in the expansion stroke and exhaust stroke after the main injection, with the same EGR rate and air-fuel ratio setting as in the normal combustion mode. In this mode, the fuel is injected three times for convenience. This temperature increase multi-injection mode is performed in order to raise the catalyst bed temperature to a temperature necessary for increasing the catalyst bed temperature by adding exhaust fuel in the PM regeneration control and S poison recovery control. Incidentally, this temperature rising multi-injection mode is basically a kind of the normal combustion mode.

<Low-temperature combustion lean mode>
The low-temperature combustion lean mode is one of the low-temperature combustion modes in which combustion is performed at a higher EGR rate than the above-described EGR rate at which the smoke emission amount reaches a peak by introducing a large amount of EGR. This low-temperature combustion lean mode is implemented mainly for the purpose of increasing the catalyst bed temperature at a low rotational speed and low load range, and reducing NOx emissions. In the low-temperature combustion lean mode, the base air-fuel ratio is set in a range of about 19 to 21, and the main injection timing is advanced as compared with the normal combustion mode so as to favorably maintain the combustion state under a high EGR rate. The injection pressure is increased. In this internal combustion engine 10, under such a high EGR rate, the combustion is slow and the effect of pilot injection is low, and the smoke emission amount may increase due to the pilot injection. Does not implement.

<Low-temperature combustion stoichiometric mode>
The low-temperature combustion stoichiometric mode is one of low-temperature combustion modes in which large-scale EGR introduction is performed in the same manner as the low-temperature combustion lean mode, and is performed to ensure the environmental conditions necessary for SOx release during the S poison recovery control. The In the low-temperature combustion stoichiometric mode, the base air-fuel ratio is set in a range of about 17 to 21, and the exhaust air-fuel ratio is made the stoichiometric air-fuel ratio by adding the exhaust fuel from the addition valve 46. Also in the low-temperature combustion stoichiometric mode, as in the low-temperature combustion lean mode, the main injection timing is advanced and the injection pressure is increased, and pilot injection is prohibited.

Next, fuel injection pressure control in the internal combustion engine 10 configured as described above will be described with reference to FIGS.
The fuel injection pressure control in the internal combustion engine 10 is basically performed as follows. That is, first, the target injection pressure is calculated based on the engine operating conditions determined by the engine speed and the engine load (fuel injection amount). The rail pressure of the common rail 42 is feedback-controlled through adjustment of the discharge amount of high-pressure fuel from the fuel pump 43 and the relief amount of high-pressure fuel by the relief valve 47 so that the calculated target injection pressure is obtained.

  By the way, in the internal combustion engine 10 that operates while switching the combustion mode as described above, the control state of the injection system and the intake system is different, so the degree of combustion activity in the combustion chamber 13 is greatly different for each combustion mode. . For example, in the normal combustion mode, the combustion is easily activated as compared with the low temperature combustion lean / stoichiometric mode in which the combustion becomes slow due to the introduction of a large amount of EGR. In such a normal combustion mode, if the EGR introduction is stopped, that is, if the EGR cut is made, the combustion is excessively activated, and the combustion noise may be deteriorated. Incidentally, the deterioration of the combustion sound here is not determined based only on the absolute value of the combustion sound level but is determined based on a relative relationship with other noises. That is, the combustion noise level that is considered to be deteriorated is different when other noise is low, such as during idle operation, and when other noise is high, such as during high-speed operation.

  In this embodiment, the problem of deterioration of combustion noise is determined based on the combustion mode, the opening degree of the EGR valve, and the like to determine whether or not the operation state in which combustion noise is likely to deteriorate due to activation of combustion as described above is determined. I am doing so. When it is determined that the vehicle is in such an operating state, combustion noise reduction control is performed to reduce the combustion noise by reducing the fuel injection pressure from the injector 40 more than usual. Such a reduction in the injection pressure suppresses atomization of the injected fuel and acts on the side that inactivates the fuel. Therefore, if the injection pressure is reduced in the above operating condition, activation of combustion can be suppressed and deterioration of combustion noise can be suppressed.

  FIG. 2 shows a flowchart of a target injection pressure calculation routine in the present embodiment. The processing of this routine is periodically executed by the electronic control device 50 during engine operation as scheduled interruption processing.

  When the processing of this routine is started, the electronic control unit 50 first determines in steps 100 to 108 whether or not there is an operating condition in which combustion is activated and the combustion noise is likely to deteriorate. Here, when all of the following (a) to (e) are established, it is determined that the vehicle is in such a driving situation.

  (A) Normal combustion mode (100: YES). As described above, in the normal combustion mode, the combustion is more easily activated than in the other combustion modes, and therefore, it is added to the above-described determination conditions.

  (B) The atmospheric pressure is not less than the predetermined value A (102: YES). When the internal combustion engine 10 is operated at a low atmospheric pressure such as a high altitude, the injection pressure is not reduced because combustion tends to become unstable due to a reduction in the intake air amount.

  (C) The engine load (fuel injection amount) is equal to or greater than a predetermined value B (104: YES). At the time of low load operation where the fuel injection amount is less than the predetermined value B, the combustion state is likely to deteriorate due to the reduction of the injection pressure, so the injection pressure is not reduced.

  (D) The EGR valve opening is equal to or less than a predetermined value C. If the EGR valve opening is small, that is, if the EGR amount is small, the combustion is easily activated. Therefore, such an upper limit condition of the EGR valve opening is added to the determination condition. In this embodiment, the predetermined value C is the fully closed opening (opening = 0) of the EGR valve 36, and the determination condition is that the EGR valve opening is fully closed. Yes.

  (E) The cooling water temperature is equal to or higher than the predetermined value D1 and lower than the predetermined value D2. In the EGR control of the internal combustion engine 10, the cooling water temperature at the time of cold start and immediately after the cooling water temperature is less than the predetermined value D1, or the cooling water temperature at which there is a possibility of overheating is higher than the predetermined value D2, EGR cut is performed. In such a situation, the EGR valve opening is always fully closed, and the above condition (d) is always satisfied. Therefore, there is a possibility that the combustion noise reduction control may be executed in an unintended operation range. The water temperature condition is added to the above judgment condition.

  If any one of the above (a) to (e) is not established, the electronic control unit 50 advances the process to step 110, and turns off the combustion noise reduction control request flag exegrnoi in step 110. Then, in the following step 115, the electronic control unit 50 calculates the target injection pressure pctrg using the normal calculation map MAP1, and once ends the processing of this routine.

  On the other hand, if all of the above (a) to (e) are satisfied, the electronic control unit 50 advances the process to step 120, and turns on the combustion noise reduction control request flag exegrnoi in step 120. In step 125, the electronic control unit 50 calculates the target injection pressure pctrg using the calculation map MAP2 for combustion noise reduction control, and once ends the processing of this routine.

  FIG. 3 shows a configuration example of the normal calculation map MAP1. As shown in the figure, the normal calculation map MAP1 is a two-dimensional map having the engine speed ne and the fuel injection amount qfin as arguments, and each engine speed NE1, NE2,..., NEn and each fuel injection amount QFIN1. , QFIN2,..., QFINm are stored as map values PCTRG11,.

  FIG. 4 shows a configuration example of the calculation map MAP2 for the combustion noise reduction control. This calculation map MAP2 is also a two-dimensional map similar to the normal calculation map MAP1, and is a target for each combination of each engine speed NE1, NE2,..., NEn and each fuel injection amount QFIN1, QFIN2,. The optimum value of the injection pressure pctrg is stored as a map value.

  A region R2 in the calculation map MAP2 shown in the figure shows engine operating conditions in which deterioration of combustion noise occurs under an operating condition where all of the above (a) to (e) are established. Region R1 indicates other engine operating conditions, that is, engine operating conditions in which the combustion noise does not deteriorate even under the above operating conditions, or noise other than the combustion noise is large and deterioration of the combustion noise does not become a problem. In the map value of the region R1 in the calculation map MAP2 for combustion noise reduction control, the same value as the normal calculation map MAP1 under the same engine operating condition is registered. On the other hand, in the region R2, a lower pressure value than the normal calculation map MAP1 under the same engine operating condition is registered as a map value.

  As described above, in an operation situation where all of the above (a) to (e) are established, the calculation map used for calculating the target injection pressure pctrg is switched from the normal calculation map MAP1 to the calculation map MAP2 for the combustion noise reduction control. It is done. Then, through the switching of the calculation map, the target injection pressure pctrg is reduced in the driving situation in which the above (a) to (e) are both established as compared with the case where it is not.

  In the present embodiment, the normal calculation map MAP1 corresponds to the first calculation map, and the calculation map MAP2 for combustion noise reduction control corresponds to the second calculation map. When all of the above (a) to (e) are established, the processing of the target injection pressure calculation routine for switching the calculation map and reducing the target injection pressure pctrg corresponds to the processing of the reducing means.

  As described above, in this embodiment, when all of the above (a) to (e) are established, the combustion pressure reduction control is performed to reduce the injection pressure and reduce the combustion noise. At the start and end of the reduction control, the target injection pressure pctrg is largely changed stepwise with the switching of the calculation map. Such a sudden change in the target injection pressure pctrg is significantly larger than the rate of change in the target injection pressure pctrg in accordance with a change in normal engine operating conditions, so that the stability of the feedback control of the rail pressure is impaired, There is a risk of overshoot and hunting.

  On the other hand, when the above (d) is not satisfied, that is, when the combustion noise reduction control is terminated in response to the resumption of EGR introduction from the EGR cut, the EGR valve 36 is caused by the flow delay of the EGR gas in the EGR path. After opening the valve, it takes a certain amount of time until EGR introduction is actually started. Therefore, for a while after the above (d) is not established, the state where EGR introduction has not yet been made continues, and if the reduced injection pressure is restored to the original value during this period, the combustion noise will be worsened. Become.

  Therefore, in the present embodiment, in the injection pressure command value calculation routine, the target injection pressure pctrg calculated in the target injection pressure calculation routine is subjected to gradual change processing after the start and end of the combustion noise reduction control. The injection pressure command value tpc, which is the final target injection pressure used for the actual feedback control, is obtained. The calculation of the injection pressure command value tpc in this injection pressure command value calculation routine is performed as follows.

First, when the target injection pressure pctrg after the start of the combustion noise reduction control is changed to the reduced pressure side, the injection pressure command value tpc is calculated in the following manner.
(A) When the required pressure reduction amount (subtraction value of the previous value tpc [i-1] of the injection pressure command value with respect to the target injection pressure pctrg) exceeds a predetermined value E (for example, 5 MPa), the injection pressure command value at this time tpc is calculated as a subtraction value of the predetermined value E from the previous value of the injection pressure command value tpc, as shown in the following equation (1). In the following equation (1), tpc [i] is the injection pressure command value calculated in the current control cycle, and tpc [i-1] is the previous value of the injection pressure command value, that is, the previous control cycle. Each calculated injection pressure command value is shown. That is, at this time, regardless of the required pressure reduction amount of the injection pressure, the injection pressure command value tpc is gradually changed so that the predetermined value E is changed to the pressure reduction side every control cycle of this routine. Become. The predetermined value E at this time is such that the rate of change of the injection pressure command value tpc (the amount of change of the injection pressure command value tpc per unit time) can maintain the stability of the feedback control of the rail pressure. Is set to that value. Incidentally, the rate of change of the injection pressure command value tpc at this time can be obtained as a division value (E / ΔT) of the predetermined value E by the execution period ΔT of this routine. In the present embodiment, the rate of change (E / ΔT) of the injection pressure command value tpc to the reduced pressure side at this time corresponds to the first rate of change.

tpc [i] ← tpc [i-1] -E (1)

(B) When the required pressure reduction amount of the injection pressure is equal to or less than the predetermined value E At this time, the gradual change processing of the injection pressure command value tpc in (A) is finished, and the target injection calculated in the target injection pressure calculation routine The value of the pressure pctrg is set as it is as the injection pressure command value tpc.

  Further, when the target injection pressure pctrg after the end of the combustion noise reduction control is changed to the pressure increasing side, and the elapsed time after the end of the combustion noise reduction control, that is, the gradual change processing period is less than the predetermined value Ta, The injection pressure command value tpc is calculated in the following manner.

(C) When the required increase amount of the injection pressure (the subtraction value of the target injection pressure pctrg with respect to the previous value tpc [i−1] of the injection pressure command value) exceeds a predetermined value F (for example, 2 MPa), the injection pressure command at this time The value tpc is calculated as an addition value of the previous value of the injection pressure command value tpc and the predetermined value F as shown in the following equation (2). That is, at this time, the injection pressure command value tpc is gradually changed so as to be changed to the pressure increase side by the predetermined value F every control cycle of this routine regardless of the magnitude of the required increase amount of the injection pressure. It becomes. Note that the predetermined value F at this time is the rate of change of the injection pressure command value tpc to the extent that combustion noise does not deteriorate even when the resumption of EGR introduction is delayed due to the response delay of the intake system. The value is set so as to limit, and the value is smaller than the predetermined value E (F <E). Incidentally, in this embodiment, the rate of change (F / ΔT) of the injection pressure command value tpc to the pressure increasing side at this time corresponds to the second rate of change.

tpc [i] ← tpc [i−1] + F (2)

(D) When the required pressure increase amount of the injection pressure is equal to or less than the predetermined value F At this time, the gradual change process of the injection pressure command value tpc in (C) is finished, and the target calculated by the target injection pressure calculation routine is completed. The value of the injection pressure pctrg is set as the injection pressure command value tpc as it is.

  Further, when the gradual change processing period after the end of the combustion noise reduction control is equal to or longer than the predetermined time Ta and the gradual change processing in (C) is continued, the injection pressure command value tpc is calculated in the following manner. The

(E) When the required pressure increase amount of the injection pressure exceeds a predetermined value E The injection pressure command value tpc at this time is the previous value of the injection pressure command value tpc and the predetermined value as shown in the following equation (3). Calculated as an addition value to E. That is, at this time, the injection pressure command value tpc is gradually changed so as to be changed to the pressure increase side by the predetermined value E every control cycle of this routine regardless of the magnitude of the required increase amount of the injection pressure. It becomes. The change rate (E / ΔT) of the injection pressure command value tpc at this time is the same as in the case of (A) above. Incidentally, in this embodiment, the rate of change (E / ΔT) of the injection pressure command value tpc to the pressure increase side at this time corresponds to the third rate of change.

tpc [i] ← tpc [i-1] + E (3)

(F) When the required increase amount of the injection pressure is equal to or less than the predetermined value E At this time, the gradual change process of the injection pressure command value tpc in (E) is finished, and the target calculated by the target injection pressure calculation routine is completed. The value of the injection pressure pctrg is set as the injection pressure command value tpc as it is.

  When none of the above (A) to (F) is applicable, the gradual change process is not performed, and the value of the target injection pressure pctrg calculated in the target injection pressure calculation routine is directly used as the injection pressure command value tpc. Is set.

  FIG. 5 shows a flowchart of the injection pressure command value routine described above. The processing of this routine is executed by the electronic control unit 50 following the target injection pressure calculation routine. In the present embodiment, the process of this routine corresponds to the process of the gradual change means.

  When the routine shifts to the routine, first, at step 200, the electronic control unit 50 switches the combustion noise reduction control request flag exegrnoi (ON → OFF or between the previous processing cycle of the routine and the current processing cycle). It is determined whether or not there has been an OFF → ON). If there is such a flag switch (YES), the electronic control unit 50 turns on the gradual change processing flag in step 205 and then proceeds to step 210. If the flag has not been switched (NO), the electronic control unit 50 proceeds to step 210 as it is.

  In step 210, the electronic control unit 50 determines whether or not the gradual change processing flag is on. If the gradual change process flag is not on (YES), the electronic control unit 50 proceeds to step 220; otherwise (NO), the process proceeds to step 215.

  In step 215, the electronic control unit 50 calculates the injection pressure command value tpc without performing the gradual change process. That is, the target injection pressure pctrg calculated by the target injection pressure calculation routine is set as it is as the injection pressure command value tpc at this time. Thereafter, the electronic control unit 50 once ends the processing of this routine.

  On the other hand, in step 220, the electronic control unit 50 determines whether or not the combustion noise reduction control request flag exegrnoi is on and the required pressure reduction amount (pctrg-tpc) exceeds the predetermined value E, that is, ( It is determined whether or not the situation of A) is applicable. If a negative determination is made here (NO), the electronic control unit 50 advances the process to step 230. When an affirmative determination is made (YES), the electronic control unit 50 advances the process to step 225, calculates the injection pressure command value tpc according to the above equation (1) in step 225, and then ends the process of this routine once. To do.

  In step 230, the electronic control unit 50 determines whether or not the combustion noise reduction control request flag exegrnoi is off and the elapsed time after the off, that is, the gradual change processing period is less than a predetermined value Ta. If an affirmative determination is made here (YES), the electronic control unit 50 proceeds to step 240. If a negative determination is made (NO), the electronic control unit 50 proceeds to step 250.

  In step 240, it is determined whether or not the required pressure increase amount (tpc−pctrg) exceeds the predetermined value F, that is, whether or not the situation (C) is satisfied. If an affirmative determination is made here (YES), the electronic control unit 50 advances the process to step 245, calculates the injection pressure command value tpc according to the above equation (2) in step 245, and then ends the process of this routine once. To do.

  In step 250, the electronic control unit 50 determines whether or not the combustion noise reduction control request flag exegrnoi is off and the required pressure increase amount (tpc-pctrg) exceeds the predetermined value E, that is, (F ) Is determined as to whether or not the situation. If the determination is affirmative (YES), the electronic control unit 50 advances the process to step 255, calculates the injection pressure command value tpc according to the above equation (3) in step 255, and then ends the process of this routine once. To do.

  If a negative determination is made in either step 240 or step 250, it corresponds to one of the situations (B), (D), and (E). Therefore, in this case, the electronic control unit 50 advances the process to step 260, and turns off the gradual change flag in step 260. Thereafter, the electronic control unit 50 advances the process to step 215, calculates the injection pressure command value tpc without performing the gradual change process, and then ends the process of this routine once.

FIG. 6 shows an example of an injection pressure control mode related to the combustion noise reduction control in the present embodiment described above.
In the example shown in the figure, at time t1, the combustion noise reduction control request flag exegrnoi is switched from OFF to ON when the EGR valve opening is fully closed to perform EGR cut. At the same time, the target injection pressure pctrg is reduced from the map value pctrg [MAP1] of the normal calculation map MAP1 to the map value pctrg [MAP2] of the calculation map MAP2 for the combustion noise reduction control.

  At this time t1, the gradual change process flag is turned on, and the gradual change process of the injection pressure command value tpc is started. The injection pressure command value tpc is thereafter directed toward the reduced target injection pressure pctrg. Each time the control period of the injection pressure command value calculation routine is changed, the pressure is changed to the reduced pressure side at a relatively rapid change rate (E / ΔT) of the predetermined value E. When the injection pressure command value tpc is reduced until the required pressure reduction amount becomes equal to or less than the predetermined value E at time t2, the gradual change processing flag is turned off, and then the injection pressure command value tpc is equal to the target injection pressure pctrg. Equivalent.

  When the EGR valve 36 is opened to resume the introduction of EGR at the subsequent time t3, the combustion noise reduction control request flag exegrnoi is switched from on to off. After the EGR valve 36 is opened, the actual increase in the EGR rate is after a certain amount of time has elapsed due to the response delay of the intake system.

  With the switching of the combustion noise reduction control request flag exegrnoi at time t3, the gradual change flag is turned on again, and the target injection pressure pctrg is set to the map value pctrg [MAP2] of the calculation map MAP2 for the combustion noise reduction control. To the map value pctrg [MAP1] of the normal calculation map MAP1.

  At this time t3, the gradual change processing flag is turned on, and the gradual change processing of the injection pressure command value tpc is started. The injection pressure command value tpc is thereafter directed toward the increased target injection pressure pctrg. Every time the injection pressure command value calculation routine is controlled, the pressure is changed to the pressure increasing side at a relatively gradual change rate (F / ΔT) of the predetermined value F.

  When the elapsed time from time t3 reaches time t4 when the predetermined value Ta is reached, the EGR rate is increased to a certain value. After this time t4, the injection pressure command value tpc is changed to the pressure increasing side at a relatively rapid change rate (E / ΔT) of the predetermined value E for each control cycle.

  At time t5, when the injection pressure command value tpc is increased until the required pressure increase amount becomes equal to or less than the predetermined value E, the gradual change processing flag is turned off, and then the injection pressure command value tpc is set to the target injection. It is set to the same value as the pressure pctrg.

In the present embodiment, the normal combustion mode corresponds to the specific combustion mode, and the other three combustion modes correspond to the other combustion modes.
In the present embodiment described above, the following effects can be obtained.

  (1) In this embodiment, the injection pressure is gradually reduced when the injection pressure (injection pressure command value tpc) at the start of the combustion noise reduction control is changed to the reduced pressure side and the injection pressure at the end is changed to the increased pressure side. Therefore, the stability of the feedback control of the rail pressure (injection pressure) can be suitably maintained regardless of the sudden change request of the injection pressure accompanying the implementation of the combustion noise reduction control.

  (2) In the present embodiment, at the end of the combustion noise reduction control accompanying the opening of the EGR valve 36, the rate of change (F / ΔT) is relatively low until the elapsed time after the end reaches the predetermined value Ta. The injection pressure is gradually changed to the pressure increase side, and thereafter, the injection pressure is gradually changed to the pressure increase side at a relatively rapid rate of change (E / ΔT) to return the injection pressure to the original value. Therefore, regardless of the response delay of the EGR rate after the EGR valve 36 is opened, the injection pressure can be restored to the original value relatively quickly while suppressing the deterioration of the combustion noise.

  (3) EGR valve opening upper limit condition (EGR valve opening is a fully closed opening), atmospheric pressure lower limit condition, and normal combustion that tends to cause combustion activation as execution conditions for combustion noise reduction control Since the operation in the mode is included, it is possible to reduce the injection pressure in an appropriate operation condition and to accurately suppress the deterioration of the combustion noise.

  (4) The injection pressure is reduced by switching the calculation map for calculating the target injection pressure pctrg from the normal calculation map MAP1 to the calculation map MAP2 for combustion noise reduction control. The deterioration of the combustion noise due to can be easily and accurately performed.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, the pressure change side / pressure reduction side of the injection pressure command value tpc with the same rate of change in the situation corresponding to (A) above and in the situation applicable to (F) above. However, it is also possible to use a different rate of change. For example, if there is a difference in the stability of the injection pressure control system against a sudden change in the injection pressure between when the injection pressure is changed to the pressure increase side and when the injection pressure is changed to the pressure reduction side, the different rate of change is set. Thus, the stability of the injection pressure control system can be more effectively maintained.

In the above embodiment, the injection pressure command value tpc is periodically increased or decreased by a predetermined value to perform the gradual change processing of the injection pressure at the start and end of the combustion noise reduction control. You may change the aspect of a process suitably. For example, even when the target injection pressure pctrg is subjected to the following weighted average process, so-called annealing process, to obtain the injection pressure command value tpc, the gradual change process can be performed. The injection pressure command value tpc in this case can be obtained by the following equation (4), for example. Specifically, (1-n) is set for the injection pressure command value tpc [i-1] obtained in the previous control cycle, and n is set for the target injection pressure pctrg calculated in the current control cycle. , Each is weighted, and the added value is calculated as the injection pressure command value tpc [i] in the current control cycle. Note that the coefficient n is a coefficient that determines the rate of change of the injection pressure command value tpc to be gradually changed, and a value greater than 0 and less than or equal to 1 is set as the value (0 <n ≦ 1). As the coefficient n is larger, that is, closer to 1, the rate of change of the injection pressure command value tpc during the gradual change increases, and the followability of the injection pressure command value tpc with respect to the target injection pressure pctrg increases. Incidentally, when the gradual change processing of the injection pressure command value tpc is performed by the following equation (4), the coefficient n in the situation corresponding to the above (C) is the same as that when the above corresponding to the above (A) and (E). By setting the value closer to 0 compared to the coefficient n, the injection pressure command value tpc can be gradually changed with the same change tendency as in the above embodiment.

tpc [i] ← (1-n) × tpc [i−1] + n × pctrg (4)

In the above embodiment, the injection pressure related to the suppression of the deterioration of the combustion noise is reduced by switching the calculation map for calculating the target injection pressure pctrg. However, for example, a constant from the target injection pressure, or activation of combustion The injection pressure reduction mode may be changed as appropriate, such as subtracting a variable based on the control amount related to.

  In the above embodiment, the EGR valve opening is a fully closed opening as one of the execution conditions of the combustion noise reduction control, but this is the upper limit condition of the EGR valve opening, that is, the EGR valve opening. May be changed to be less than or equal to a predetermined value. Even if the opening degree is not fully closed, if the EGR valve opening degree is sufficiently small and the amount of EGR is not sufficiently small, combustion is likely to be activated.

  -Of the above (a) to (e), which are the execution conditions of the combustion noise reduction control, conditions other than (d) may be omitted. In addition, if there is another appropriate condition that indicates an operating condition in which combustion noise is likely to deteriorate, it may be added to the execution condition.

1 is a schematic diagram showing the overall structure of an internal combustion engine to which an embodiment of the present invention is applied. The flowchart of the request | requirement injection pressure calculation routine employ | adopted as the same embodiment. The figure which shows the structural example of the calculation map for normal used for the target injection pressure calculation in the same embodiment. The figure which shows the structural example of the calculation map for combustion noise reduction control used for the target injection pressure calculation in the same embodiment. Flow chart of target injection pressure calculation routine employed in the same embodiment The time chart which shows an example of the control aspect of the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Turbocharger, 12 ... Intake passage, 13 ... Combustion chamber, 14 ... Exhaust passage, 15 ... Air cleaner, 16 ... Air flow meter, 17 ... Compressor, 18 ... Intercooler, 19 ... Intake throttle valve, 20 DESCRIPTION OF SYMBOLS ... Intake manifold, 21 ... Intake port, 22 ... Exhaust port, 23 ... Exhaust manifold, 24 ... Exhaust turbine, 25 ... NOx catalytic converter, 26 ... PM filter, 27 ... Oxidation catalytic converter, 28 ... Incoming gas temperature sensor, 29 ... Outgas temperature sensor, 30 ... Differential pressure sensor, 31, 32 ... Oxygen sensor, 33 ... EGR passage, 34 ... EGR catalyst, 35 ... EGR cooler, 36 ... EGR valve, 40 ... Injector, 41 ... High pressure fuel supply pipe, 42 ... Common rail, 43 ... Fuel pump, 44 ... Rail pressure sensor, 45 ... Low pressure fuel supply pipe, 46 ... Addition valve 47 ... relief valve, 50 ... electronic control unit, 51 ... NE sensor 52: accelerator sensor, 53 ... throttle valve sensor, 54 ... atmospheric pressure sensor.

Claims (5)

In a fuel injection control device for an internal combustion engine, which is applied to an internal combustion engine including an exhaust gas recirculation valve that adjusts an exhaust gas recirculation amount into intake air and controls an injection pressure of fuel supplied to combustion,
When it is determined that the operation condition is likely to deteriorate the combustion noise when a predetermined condition including the upper limit condition of the opening degree of the exhaust gas recirculation valve is satisfied, Reducing means for reducing the injection pressure;
The injection pressure is gradually changed at the first rate of change when the injection pressure is changed to the pressure reducing side at the start of the injection pressure reduction by the reduction means, and the reduction of the injection pressure by the reduction means is completed. When the injection pressure is changed to the pressure increase side, the injection pressure is increased to the pressure increase side at a second change rate smaller than the first change rate for a predetermined period from when the predetermined condition is not satisfied. Gradually changing means for gradually changing, and thereafter gradually changing the injection pressure at a third rate of change greater than the second rate of change;
A fuel injection control device for an internal combustion engine, comprising: The fuel injection control device for an internal combustion engine according to claim 1, wherein the upper limit opening degree in the upper limit condition of the opening degree of the exhaust gas recirculation valve is a fully closed opening degree of the exhaust gas recirculation valve. The internal combustion engine operates while switching the combustion mode between a plurality of combustion modes,
The predetermined condition includes being in operation in a specific combustion mode in which a combustion state is more easily activated than the other combustion modes among the plurality of combustion modes. Fuel injection control device for internal combustion engine. The fuel injection control device for an internal combustion engine according to any one of claims 1 to 3, wherein the predetermined condition includes a lower limit condition of atmospheric pressure. As the calculation map of the injection pressure based on the engine operating condition, the first calculation map and the first map that is set so that the map value of the injection pressure under the same engine operating condition is smaller than that of the first calculation map. The injection pressure is reduced by the reducing means by switching the calculation map used for calculating the injection pressure from the first calculation map to the second calculation map. The fuel injection control device for an internal combustion engine according to any one of -4.

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