JP2006029273A - Egr system of internal combustion engine for vehicle with supercharger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR system of an internal combustion engine for a vehicle with a supercharger, improving the accelerating performance of the vehicle and also improving exhaust emission. <P>SOLUTION: This EGR system of the internal combustion engine for the vehicle with the supercharger, provided with an EGR passage 11 connecting an exhaust passage 4 with an intake passage 3 farther upstream of the supercharger 8, and an EGR valve 12 adjusting a flow rate of gas flowing in the EGR passage, is provided with an intake pressure adjusting means 6 arranged in the intake passage farther upstream of the supercharger and increasing intake pressure by compressing air, a bypass passage 7 bypassing the intake pressure adjusting means, and a bypass valve 9 adjusting a flow rate of intake air flowing in the bypass passage. The EGR passage is connected to the intake passage between the intake pressure adjusting means and the supercharger. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an EGR system for a vehicle internal combustion engine with a supercharger.

An apparatus is known in which EGR gas is recirculated from an exhaust passage downstream of a catalyst to an intake passage downstream of a throttle valve and upstream of a compressor of a turbocharger to expand a low-temperature combustion region to a high load operation side (see Patent Document 1). . In addition, there is Patent Document 2 as a prior art document related to the present invention.
JP 2000-008835 A Special table 2001-509561 gazette

  In the EGR system that recirculates exhaust from the exhaust passage downstream of the catalyst to the intake passage upstream of the compressor of the turbocharger, the length of the EGR passage becomes long, so that the exhaust remaining in the EGR passage during acceleration of the vehicle or the like The introduction of a large amount of air into the vehicle delays the introduction of fresh air, which may deteriorate vehicle acceleration and exhaust emissions.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an EGR system for a vehicle internal combustion engine with a supercharger that can improve the acceleration of the vehicle and improve the exhaust emission.

  An EGR system for an internal combustion engine for a vehicle with a supercharger according to the present invention includes an EGR passage that connects an exhaust passage and an intake passage upstream of the supercharger, and an EGR valve that adjusts the flow rate of gas flowing through the EGR passage. And an intake pressure adjusting means that is arranged in an intake passage upstream of the supercharger and compresses air to increase the intake pressure, and A bypass passage that bypasses the air pressure adjusting means, and a bypass valve that adjusts a flow rate of the intake air flowing through the bypass passage, wherein the EGR passage is an intake passage between the intake pressure adjusting means and the supercharger The above-described problem is solved by being connected to the terminal (Claim 1).

  According to the EGR system of the present invention, only the supercharger can be operated by stopping the intake pressure adjusting means and opening the bypass valve during steady operation of the internal combustion engine. Thus, by operating only the supercharger, EGR gas (exhaust gas recirculated from the exhaust passage to the intake passage) can be introduced into the intake passage to the high load operation region of the internal combustion engine by the supercharger. Therefore, exhaust emission can be improved. The intake pressure can be increased by the intake pressure adjusting means and the supercharger by operating the intake pressure adjusting means and closing the bypass valve when the vehicle is accelerated. Further, since the pressure in the intake passage between the intake pressure adjusting means and the supercharger is increased by the operation of the intake pressure adjusting means, it is possible to prevent the EGR gas from flowing into the intake passage. Therefore, fresh air can be introduced quickly into the internal combustion engine, and the EGR gas remaining in the intake passage can be quickly supplied to the internal combustion engine, so that the acceleration of the vehicle can be improved.

  In the EGR system for an internal combustion engine for a vehicle with a supercharger according to the present invention, the vehicle is required to be accelerated, and a predetermined EGR gas introduction stop condition for stopping the introduction of EGR gas into the intake passage is satisfied. If it is determined that there is an EGR control means for closing the bypass valve and operating the intake pressure adjusting means (Claim 2). Thus, by closing the bypass valve and operating the intake pressure adjusting means to increase the intake pressure, the intake pressure upstream of the supercharger can be increased. Therefore, for example, even if the timing for closing the EGR valve is delayed, the flow of EGR gas into the intake passage can be suppressed by the increase of the intake pressure, so that the introduction of fresh air into the internal combustion engine is promoted and the acceleration performance is improved. Can do.

  In the EGR system for a vehicle internal combustion engine with a supercharger according to the present invention, when acceleration is required for the vehicle in an operating state in which the EGR valve is opened and EGR gas is recirculated to the intake passage, The bypass valve is closed, and after the vehicle is accelerated, the operation state of the internal combustion engine shifts to an EGR gas introduction stop operation region where the introduction of EGR gas is stopped, or an EGR gas introduction operation region where EGR gas is introduced When the operation state of the internal combustion engine is determined to shift to the EGR introduction stop operation region, the EGR valve is fully closed, and when it is determined to shift to the EGR introduction operation region, the EGR valve EGR control means for maintaining the opening degree may be provided (claim 3). When the operating state of the internal combustion engine shifts to the EGR introduction operation region after the vehicle is accelerated, the intake air between the intake pressure adjusting means and the supercharger is maintained rather than the exhaust passage pressure by maintaining the opening of the EGR valve. EGR gas can be introduced into the intake passage until the pressure in the passage becomes higher. Therefore, EGR gas can be introduced without controlling the EGR valve with high accuracy. Further, it is possible to maintain the EGR valve open by determining whether the EGR valve is closed after the bypass valve is closed. Therefore, the intake pressure can be increased by closing the bypass valve and the EGR valve can be kept open to introduce the EGR gas into the intake passage. Therefore, the acceleration of the vehicle can be improved and the exhaust emission can be improved.

  In the EGR system for a vehicle internal combustion engine with a supercharger according to the present invention, when the EGR control means determines that the operation state of the internal combustion engine shifts to the EGR gas introduction stop operation region after the acceleration of the vehicle, Comparing the exhaust pressure of the passage and the intake pressure of the intake passage between the intake pressure adjusting means and the supercharger, if the intake pressure is high, the EGR valve is closed after a predetermined time, When the exhaust pressure is high, the EGR valve may be closed immediately (Claim 4). By operating the EGR valve in this manner, fresh air can be introduced into the EGR passage and the EGR gas in the EGR passage can be discharged to the exhaust passage. Therefore, since EGR gas remaining in the EGR passage can be prevented or reduced, corrosion of the EGR passage due to EGR gas can be suppressed.

  In the EGR system for an internal combustion engine for a vehicle with a supercharger according to the present invention, the EGR control means determines that the operation state of the internal combustion engine shifts to the EGR gas introduction stop operation region after acceleration of the vehicle. It is estimated whether or not the intake pressure in the intake passage between the intake pressure adjusting means and the supercharger is higher than the exhaust pressure in the passage, and when it is estimated that the intake pressure is higher The EGR valve may be closed (Claim 5). By closing the EGR valve in this manner, even when the intake pressure becomes higher than the exhaust pressure or when the state changes so that the intake air pushes the EGR gas in the EGR passage to the exhaust passage, the EGR valve EGR gas can be left in the EGR passage closer to the intake passage. Therefore, the next time EGR gas is introduced, EGR gas can be quickly introduced into the intake passage.

  In the EGR system for a vehicle internal combustion engine with a supercharger according to the present invention, when acceleration is required for the vehicle in an operating state in which the EGR valve is opened and EGR gas is recirculated to the intake passage, The bypass valve is controlled and the vehicle is accelerated so that the pressure difference between the exhaust pressure in the exhaust passage and the intake pressure in the intake passage between the intake pressure adjusting means and the supercharger is maintained at a predetermined value. EGR control means for closing the EGR valve may be provided when it is determined that the operation state of the internal combustion engine will shift to an EGR gas introduction / stop operation region where the introduction of EGR gas is stopped later (Claim 6). In this way, by adjusting the bypass valve so that the pressure difference is maintained at a predetermined value, EGR gas can be introduced into the intake passage even during acceleration of the vehicle, so that exhaust emission during acceleration can be improved. Further, by adjusting the pressure difference so that the sensitivity of the change in the EGR gas amount due to the change in the pressure difference is higher than the sensitivity of the change in the EGR gas amount due to the adjustment of the opening degree of the bypass valve, the introduction delay or EGR of the EGR gas Variations in gas amount can be suppressed.

  In the EGR system for a vehicle internal combustion engine with a supercharger according to the present invention, the EGR gas introduction stop operation region in which the intake pressure adjusting means is in an operating state and the operation state of the internal combustion engine stops the introduction of EGR gas. When it is determined to shift to an EGR gas introduction operation region where gas is introduced, the EGR valve is opened to a target opening set after the operation state of the internal combustion engine has shifted to the EGR introduction operation region, and then the bypass You may provide the EGR control means which opens a valve (Claim 7). Thus, when the operating state of the internal combustion engine shifts from the EGR introduction / stop operation region to the EGR introduction operation region, the EGR valve is opened to a target opening set in advance after the internal combustion engine operation state has shifted to the EGR introduction operation region. Then, by opening the bypass valve, the pressure of the intake passage between the intake pressure adjusting means and the supercharger decreases, and the EGR gas is quickly released when the pressure is lower than the pressure of the exhaust passage. It can be introduced into the intake passage. By suppressing the introduction delay of EGR gas in this way, exhaust emission can be improved.

  In the EGR system for a vehicle internal combustion engine with a supercharger according to the present invention, the EGR gas introduction stop operation region in which the intake pressure adjusting means is in an operating state and the operation state of the internal combustion engine stops the introduction of EGR gas. When it is determined to shift to the EGR gas introduction operation region for introducing gas, the bypass valve is opened, and then the intake pressure in the intake passage between the exhaust pressure in the exhaust passage, the intake pressure adjusting means and the supercharger is opened. EGR control means may be provided that opens the EGR valve when it is determined that the exhaust pressure is higher than the intake pressure by comparing with the pressure (Claim 8). As described above, when it is determined that the operating state of the internal combustion engine shifts from the EGR introduction / stop operation region to the EGR introduction operation region, the bypass valve is first opened, and then the EGR is determined when the exhaust pressure is determined to be higher than the intake pressure. By opening the valve, the backflow of fresh air (intake air) into the EGR passage can be prevented. Therefore, EGR gas can be left in the EGR passage, and EGR gas can be quickly introduced into the intake passage when the EGR gas is introduced next. Therefore, exhaust emission can be improved.

  As described above, according to the exhaust gas purification apparatus of the present invention, EGR gas can be quickly introduced into the intake passage when the operating state of the internal combustion engine shifts to the EGR introduction operation region. It is possible to improve the exhaust emission by suppressing the generation of. Further, when the operation state of the internal combustion engine is shifted to the EGR introduction / stop operation region such as when the vehicle is accelerated, it is possible to prevent the inflow of EGR gas from the EGR passage and to introduce fresh air into the internal combustion engine quickly. , Acceleration can be improved.

  FIG. 1 shows an embodiment in which the EGR system of the present invention is applied to a diesel engine 1 as an internal combustion engine. The engine 1 is mounted on a vehicle as a driving power source, and an intake passage 3 and an exhaust passage 4 are connected to the cylinder 2 thereof. The intake passage 3 includes an air filter 5 for intake air filtration, a supercharger (hereinafter abbreviated as S / C) 6 as intake pressure adjusting means, a bypass passage 7 bypassing the S / C 6, and a supercharger. A compressor 8a of a turbocharger (turbo supercharger) 8 is provided. The bypass passage 7 is provided with a bypass valve 9 that adjusts the flow of intake air flowing through the bypass passage 7. The exhaust passage 4 is provided with a turbine 8b of a turbocharger 8 and an exhaust purification catalyst 10 as exhaust purification means. The S / C 6 includes an electric motor 6a as a driving device. By driving the electric motor 6a, the S / C 6 operates and compresses the air in the intake passage 3 to increase the intake pressure.

  The exhaust passage 4 and the intake passage 3 are connected by an EGR passage 11, and the EGR passage 11 is provided with an EGR valve 12 that adjusts the flow rate of gas flowing through the EGR passage 11. As shown in FIG. 1, the EGR passage 11 is connected to the exhaust passage 4 downstream of the exhaust purification catalyst 10. The EGR system that extracts the exhaust gas from the downstream side of the turbine 8b of the turbocharger 8 and recirculates it to the intake passage 3 is called a so-called low pressure loop. The EGR passage 11 is connected to the intake passage 3 between the S / C 6 and the compressor 8a.

  The operations of the electric motor 6a, the bypass valve 9 and the EGR valve 12 are controlled by an engine control unit (ECU) 13, respectively. The ECU 13 is a well-known computer unit for properly operating the engine 1 by controlling the fuel injection amount, the fuel injection timing, and the like. By executing the EGR control routine of FIG. 2, the ECU 13 serves as the EGR control means of the present invention. Function. The routine of FIG. 2 is repeatedly executed at a predetermined cycle while the engine 1 is operating. Various sensors are connected to the ECU 13, and the ECU 13 performs various controls with reference to information of these sensors. As such a sensor, for example, an accelerator opening sensor 14 for detecting an accelerator opening of a vehicle on which the engine 1 is mounted and an amount of change thereof, an engine speed sensor 15 for outputting a signal corresponding to the engine speed, An intake pressure sensor 16 that outputs a signal corresponding to the pressure in the intake passage 3 downstream of the S / C 6, an air flow meter 17 that outputs a signal corresponding to the flow rate of air (fresh air) flowing into the intake passage 3, and an exhaust purification catalyst An exhaust pressure sensor 18 that outputs a signal corresponding to the pressure in the exhaust passage 4 downstream of the exhaust gas 10 is provided. These various sensors may be sensors that detect the physical quantity itself that is a detection target, or may estimate the physical quantity.

  In the EGR control routine of FIG. 2, the ECU 13 first determines in step S11 whether or not acceleration is requested for the vehicle on which the engine 1 is mounted. The acceleration request is determined based on, for example, the accelerator opening, and it is determined that acceleration is requested when the accelerator opening is increased. Further, the acceleration of the vehicle may be determined based on the state of the clutch pedal in addition to the accelerator opening. In this case, it is determined that the request is made when the clutch pedal is depressed. If it is determined that acceleration is not requested, the current routine is terminated. On the other hand, when it is determined that acceleration is required, the process proceeds to step S12, and the ECU 13 determines whether or not the introduction stop of the EGR gas is requested. Whether or not the EGR gas introduction stop is requested is determined based on, for example, the torque required for the engine 1. For example, when the torque required for the engine 1 is equal to or greater than a predetermined torque, the EGR gas introduction stop is requested. (EGR gas introduction stop condition is satisfied). As the predetermined torque, for example, a torque is set such that the vehicle cannot be accelerated properly when the EGR gas is recirculated to the intake passage 3. If it is determined that the EGR gas introduction stop is not requested, the current routine is terminated. On the other hand, if it is determined that the EGR gas introduction stop is requested, the process proceeds to step S13 where the ECU 13 fully closes the bypass valve 9 and activates the S / C 6. Thereafter, the current routine is terminated.

  In the routine of FIG. 2, when acceleration of the vehicle is required and introduction / stop of EGR gas is required, the bypass valve 9 is fully closed and the S / C 6 is operated. By operating the bypass valve 9 and the S / C 6 in this way, the S / C 6 and the compressor 8a are more effective than the exhaust pressure in the exhaust passage 4 downstream of the exhaust purification catalyst 10 (hereinafter, abbreviated as the exhaust passage pressure Pcater). The intake pressure of the intake passage 3 in the meantime (hereinafter abbreviated as intake passage pressure P1b) can be increased. This increase in the intake passage pressure P1b suppresses the introduction of EGR gas from the EGR passage 11 to the intake passage 3, promotes the introduction of fresh air into the engine 1, and removes the EGR gas remaining in the intake passage 3. The engine 1 is quickly supplied. Therefore, even if the control of the EGR valve 12 is delayed, the acceleration performance of the vehicle does not deteriorate.

  Next, another embodiment of the EGR control routine of the present invention will be described with reference to FIGS. The engine 1 is required to have various performances depending on, for example, the vehicle on which it is mounted and the driving state. For example, it is required to improve exhaust emission by rapid introduction of EGR gas or to improve the acceleration of the vehicle by introducing a large amount of fresh air when the vehicle is accelerated. Therefore, the ECU 13 executes the EGR control routine shown in FIGS. 3 to 14, and controls the electric motor 6a, the bypass valve 9, and the EGR valve 12 according to various requests.

  The routine of FIG. 3 shows a second embodiment of the EGR control routine. The routine of FIG. 3 is repeatedly executed at a predetermined cycle while the engine 1 is operating. In FIG. 3, the same processes as those in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.

  In the routine of FIG. 3, the ECU 13 first determines in step S21 whether or not the EGR rate (EGR gas amount / (new air amount + EGR gas amount)) indicating the proportion of EGR gas contained in the intake air is high. The EGR rate is determined to be high when, for example, the vehicle is stopped and the engine 1 is idle or lightly loaded. In addition, it may be determined whether or not the EGR rate is high based on the opening degree of the EGR valve 12 or the amount of fresh air sucked into the intake passage 3. If it is determined that the EGR rate is low, the current routine is terminated. On the other hand, if it is determined that the EGR rate is high, the process proceeds to step S11, and the ECU 13 determines whether or not acceleration is required for the vehicle. If it is determined that acceleration is not required for the vehicle, the current routine is terminated. On the other hand, if it is determined that acceleration is required for the vehicle, the process proceeds to step S13 where the ECU 13 fully closes the bypass valve 9 and activates S / C6.

  In the next step S22, the ECU 13 determines whether or not the operating state of the engine 1 shifts to an EGR introduction / stop operation region in which the introduction of EGR gas into the intake passage 3 is stopped after acceleration of the vehicle. Whether or not the operating state of the engine 1 shifts to the EGR introduction / stop operation region is determined with reference to, for example, a map shown in FIG. The map of FIG. 4 shows the relationship between the rotational speed and load of the engine 1 and the EGR gas introduction operation region A1 for introducing EGR gas and the EGR gas introduction stop operation region A2 for stopping the introduction of EGR gas. The relationship between the rotational speed and load of the engine 1 and the EGR gas introduction operation region A1 and the EGR gas introduction stop operation region A2 is set in advance based on experiments or the like. For example, it is assumed that the rotation speed and load of the engine 1 during acceleration of the vehicle change from the point P1 in the EGR gas introduction operation region A1 in FIG. 4 to the point P2 in the EGR gas introduction stop operation region A2 (arrow I in FIG. 4). When it is changed or changed, it is determined that the engine 1 shifts to the EGR introduction / stop operation region after acceleration of the vehicle. On the other hand, it is estimated that the rotation speed and load of the engine 1 during acceleration of the vehicle change from the point P1 in the EGR gas introduction operation region A1 in FIG. 4 to the point P3 in the same EGR gas introduction operation region A1 (arrow II in FIG. 4). If it has been changed or changed, it is determined that the engine 1 shifts to the EGR introduction operation region after the acceleration of the vehicle. In addition, estimation of the change of the driving | running state of the engine 1 is implemented based on the rotation speed of the engine 1, and the variation | change_quantity of load. When it is determined that the operation state of the engine 1 shifts to the EGR introduction / stop operation region, the process proceeds to step S23, and the ECU 13 fully closes the EGR valve 12. Thereafter, the current routine is terminated. On the other hand, when it is determined that the operation state of the engine 1 is shifted to the EGR introduction operation region, the process proceeds to step S24, and the ECU 13 maintains the opening degree of the EGR valve 12. Thereafter, the current routine is terminated.

  FIGS. 5A to 5D show the time change of the clutch switch, the time change of the opening degree of the bypass valve 9 and the EGR valve 12, the intake passage pressure P1b, and the exhaust passage pressure Pcater when the routine of FIG. 3 is executed. An example of the time change and the time change of the EGR rate is shown. The clutch switch outputs a signal corresponding to whether or not the vehicle clutch is depressed, and outputs an on signal when the clutch is depressed. In FIG. 5B, a line L1 indicates a change in the opening degree of the bypass valve 9, and a line L2 indicates a change in the opening degree of the EGR valve 12. In FIG. 5B, the valve opening degree 0 indicates fully closed, and the valve opening degree 100 indicates fully open. When the clutch switch changes to the on state at time T1 in FIG. 5 and the vehicle is requested to accelerate, the bypass valve 9 is fully closed and the S / C 6 is activated (step S13 in FIG. 3). ). When supercharging by S / C6 is performed, the intake passage pressure P1b starts to gradually increase as shown in FIG. The increase in the intake passage pressure P1b decreases the differential pressure between the intake passage pressure P1b and the exhaust passage pressure Pcater. This decrease in the differential pressure decreases the flow rate of EGR gas to the intake passage 3 and gradually decreases the EGR rate.

  As described above, in the routine of FIG. 3, the operation determination of the EGR valve 12 is delayed from the operation determination of the bypass valve 9, so that the intake passage pressure P1b becomes larger than the exhaust passage pressure Pcutter even during acceleration of the vehicle (FIG. 5). Time T2) EGR gas can be introduced into the intake passage 3 to the limit. As a result, exhaust emission during vehicle acceleration can be improved. Further, since the introduction of the EGR gas is stopped when the intake passage pressure P1b exceeds the exhaust passage pressure Pcater, the acceleration of the vehicle can be improved. Therefore, it is possible to achieve both improvement in exhaust emission and improvement in vehicle acceleration.

  The routine of FIG. 6 shows a third embodiment of the EGR control routine. The routine of FIG. 6 is repeatedly executed at a predetermined cycle while the engine 1 is operating. In FIG. 6, the same processes as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted.

  In the routine of FIG. 6, the same processing as that of the routine of FIG. 3 is performed until step S22. When it is determined in step S22 that the operating state of the engine 1 shifts to the EGR introduction / stop operation region, the process proceeds to step S31, and the ECU 13 determines whether or not the exhaust passage pressure Pcafter is less than the intake passage pressure P1b. If it is determined that the exhaust passage pressure Pcaft is less than the intake passage pressure P1b, the process proceeds to step S32, and the ECU 13 fully closes the EGR valve 12 after a predetermined time Ta has elapsed. Thereafter, the current routine is terminated. The predetermined time Ta is set based on, for example, the length of the EGR passage 11 or the differential pressure ΔT between the exhaust passage pressure Pcafter and the intake passage pressure P1b. On the other hand, when it is determined that the exhaust passage pressure Pcaft is equal to or higher than the intake passage pressure P1b, the process proceeds to step S33, and the ECU 13 immediately closes the EGR valve 12 fully. Thereafter, the current routine is terminated.

  FIGS. 7A to 7D show the time change of the clutch switch, the time change of the opening degree of the bypass valve 9 and the EGR valve 12, the intake passage pressure P1b, and the exhaust passage pressure Pcater when the routine of FIG. 6 is executed. An example of the time change and the time change of the EGR rate is shown. In FIG. 7B, the line L1 indicates the change in the opening degree of the bypass valve 9, the line L2 indicates the change in the opening degree of the EGR valve 12, the valve opening degree 0 is fully closed, and the valve opening degree 100 is fully open. Respectively. As shown in FIG. 7B, in the routine shown in FIG. 6, the bypass valve 9 is fully closed and the S / C 6 is operated at the time (time T11) when acceleration of the vehicle is requested. Thereafter, the EGR valve 12 is fully closed (time T13) after a predetermined time Ta has elapsed from the time (time T12) when the exhaust passage pressure Pcafter changes to less than the intake passage pressure P1b.

  As described above, in the routine of FIG. 6, when it is determined that the exhaust passage pressure Pcaft is less than the intake passage pressure P1b, the fresh air is introduced into the EGR passage 11 by closing the EGR valve 12 after a predetermined time Ta has elapsed. Then, the EGR gas can be discharged from the EGR passage 11. Therefore, the amount of EGR gas remaining in the EGR passage 11 can be reduced, and corrosion of the EGR passage 11 due to EGR gas can be prevented.

  The routine of FIG. 8 shows a fourth embodiment of the EGR control routine. The routine of FIG. 8 is repeatedly executed at a predetermined cycle while the engine 1 is operating. In FIG. 8, the same processes as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted.

  In the routine of FIG. 8, the same processing as that of the routine of FIG. 3 is performed until step S22. If it is determined in step S22 that the operating state of the engine 1 shifts to the EGR introduction / stop operation region, the process proceeds to step S41, and the ECU 13 estimates whether the exhaust passage pressure Pcaft changes to less than the intake passage pressure P1b. This change in pressure is estimated based on, for example, a change in the rotational speed of S / C 6 or a change amount in the intake passage pressure P1b. In the next step S42, the ECU 13 determines whether or not the exhaust passage pressure Pcaft changes below the intake passage pressure P1b based on the estimation result. If it is determined that the exhaust passage pressure Pcafter does not change below the intake passage pressure P1b, that is, the exhaust passage pressure Pcafter is maintained at the intake passage pressure P1b or higher, the current routine is terminated. On the other hand, if it is determined that the exhaust passage pressure Pcaft changes to less than the intake passage pressure P1b, the process proceeds to step S43, and the ECU 13 fully closes the EGR valve 12 so that a predetermined amount of EGR gas remains in the EGR passage 11. Thereafter, the current routine is terminated. The predetermined amount is set such that, for example, when the EGR gas is introduced next, the introduction into the intake passage 3 is not delayed by the EGR gas remaining in the EGR passage 11.

  9 (a) to 9 (d) show the time change of the clutch switch when the routine of FIG. 8 is executed, the time change of the opening degree of the bypass valve 9 and the EGR valve 12, the intake passage pressure P1b and the exhaust passage pressure Pcafter. An example of the time change and the time change of the EGR rate is shown. In FIG. 9B, the line L1 indicates the change in the opening degree of the bypass valve 9, the line L2 indicates the change in the opening degree of the EGR valve 12, the valve opening degree 0 is fully closed, and the valve opening degree 100 is fully open. Respectively. In the routine of FIG. 8, it is estimated whether the exhaust passage pressure Pcafter changes to less than the intake passage pressure P1b (step S41), and it is determined that the exhaust passage pressure Pcafter changes to less than the intake passage pressure P1b (Yes in step S42). Fully closes the EGR valve 12 (step S43). Therefore, as shown in FIG. 9B, when it is determined that the exhaust passage pressure Pcafter changes to less than the intake passage pressure P1b after the clutch switch changes to the on state at time T21 (time T22), the EGR valve 12 valve closing starts. Therefore, the EGR valve 12 can be fully closed before the intake passage pressure P1b changes to the exhaust passage pressure Pcafter or higher (time T23).

  In this way, in the routine of FIG. 8, the EGR valve 12 can be fully closed before the intake passage pressure P1b changes to the exhaust passage pressure Pcaft or higher. Therefore, even if the intake passage pressure P1b rises and fresh air flows into the EGR passage 11, EGR gas can remain in the EGR passage 11 on the intake passage 3 side of the EGR valve 12. Therefore, when the EGR gas is introduced into the intake passage 3 next time, the EGR gas remaining in the EGR passage 11 can be quickly introduced into the intake passage 3. As described above, exhaust emission can be improved by rapidly introducing EGR.

  The routine of FIG. 10 shows a fifth embodiment of the EGR control routine. The routine of FIG. 10 is repeatedly executed at a predetermined cycle while the engine 1 is operating. In FIG. 10, the same processes as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted.

  In the routine of FIG. 10, the same processing as that of the routine of FIG. 3 is performed until step S11. If it is determined in step S11 that acceleration is required for the vehicle, the process proceeds to step S51, and the ECU 13 activates S / C6. In the subsequent step S52, the ECU 13 controls the operation of the bypass valve 9 so that the differential pressure Pl obtained by subtracting the intake passage pressure P1b from the exhaust passage pressure Pcafter is maintained constant. The differential pressure Pl is an appropriate amount of EGR gas in the intake passage 3 under the condition that the sensitivity of the change in the EGR gas amount due to the change in the pressure difference is higher than the sensitivity of the change in the EGR gas amount due to the adjustment of the opening degree of the bypass valve 9. May be set so that can be introduced, or may be set by the following method. The intake passage pressure P1b is set to an upper limit value so that NOx and smoke are not discharged from the engine 1 due to supercharging. On the other hand, the lower limit value is the pressure when the S / C 6 is operated and the bypass valve 9 is fully opened. The exhaust passage pressure Pcaft varies depending on the operating state of the engine 1. Therefore, the differential pressure Pl is set such that the intake passage pressure P1b is lower than the fluctuating exhaust passage pressure Pcatter, and the intake passage pressure P1b falls between the upper limit value and the lower limit value. In the next step S22, the ECU 13 determines whether or not the state of the engine 1 shifts to the EGR introduction / stop operation region after the vehicle is accelerated. If it is determined not to shift to the EGR introduction stop operation region, the current routine is terminated. On the other hand, if it is determined to shift to the EGR introduction stop operation region, the process proceeds to step S53, and the ECU 13 fully closes the EGR valve 12 and the bypass valve 9. Thereafter, the current routine is terminated.

  FIGS. 11A to 11D show the time change of the clutch switch, the time change of the opening degree of the bypass valve 9 and the EGR valve 12, the intake passage pressure P1b, and the exhaust passage pressure Pcater when the routine of FIG. 10 is executed. An example of the time change and the time change of the EGR rate is shown. In FIG. 11B, the line L1 indicates the change in the opening degree of the bypass valve 9, the line L2 indicates the change in the opening degree of the EGR valve 12, the valve opening degree 0 is fully closed, and the valve opening degree 100 is fully open. Respectively. As shown in FIG. 11C, when acceleration of the vehicle is requested at time T31, the bypass valve 9 is once controlled to close (time T31 to T32), and thereafter the differential pressure Pl is kept constant. Thus, the opening degree is controlled (time T32 to T33). Therefore, the EGR rate can be maintained in a constant state as shown in FIG.

  As described above, in the routine shown in FIG. 10, when the vehicle is requested to accelerate, the opening degree of the bypass valve 9 is adjusted so that the differential pressure Pl is maintained constant. Therefore, even when the vehicle is accelerated, fluctuations in the EGR rate can be suppressed and EGR gas can be stably introduced into the intake passage 3. Further, since the exhaust passage pressure Pcafter is maintained higher than the intake passage pressure P1b, when the EGR gas is introduced into the intake passage 3 after the vehicle is accelerated, the EGR gas can be introduced into the intake passage 3 quickly.

  The routine of FIG. 12 shows a sixth embodiment of the EGR control routine. The routine of FIG. 12 is repeatedly executed at a predetermined cycle while the engine 1 is operating.

  In the routine of FIG. 12, the ECU 13 first determines whether or not the S / C 6 is in an operating state in step S61. If it is determined that the S / C 6 is not in an operating state, that is, is stopped, the current routine is terminated. On the other hand, when it is determined that S / C 6 is in the operating state, the process proceeds to step S62, and the ECU 13 determines whether or not the operating state of the engine 1 shifts from the EGR introduction stop operation region to the EGR introduction operation region. Whether to shift from the EGR introduction stop operation region to the EGR introduction operation region is determined with reference to, for example, the map of FIG. When it is estimated that the operating state of the engine 1 changes from the EGR introduction stop operation area A2 to the EGR introduction operation area A1 (for example, the point P2 to the point P3 in FIG. 4) in the map of FIG. 4 (arrow III in FIG. 4). Or when it changes, it is judged that the driving | running state of the engine 1 transfers to an EGR introduction | transduction operation area | region. When it is determined that the operation state of the engine 1 does not shift to the EGR introduction operation region, the current routine is terminated. On the other hand, when it is determined that the operation state of the engine 1 shifts to the EGR introduction operation region, the process proceeds to step S63, where the ECU 13 sets the opening degree of the EGR valve 12 and the EGR gas appropriately flows into the intake passage after the engine 1 moves to the EGR introduction operation region. 3 is set to an opening degree (target opening degree) as introduced in FIG. In subsequent step S64, the ECU 13 opens the bypass valve 9 so that the intake passage pressure P1b decreases. Thereafter, the current routine is terminated.

  FIGS. 13A to 13D show the time change of the EGR request signal for requesting the introduction of EGR gas into the intake passage 3 when the routine of FIG. 12 is executed, and the opening degrees of the bypass valve 9 and the EGR valve 12. An example of the time change, the time change of the intake passage pressure P1b and the exhaust passage pressure Pcater, and the time change of the EGR rate are shown. In FIG. 13B, the line L1 indicates the change in the opening degree of the bypass valve 9, the line L2 indicates the change in the opening degree of the EGR valve 12, the valve opening degree 0 is fully closed, and the valve opening degree 100 is fully open. Respectively. As shown in FIG. 13B, in the routine of FIG. 12, when it is determined that the operating state of the engine 1 shifts to the EGR introduction operating region (affirmative determination in step S62), the EGR request signal is turned on. The valve opening of the EGR valve 12 is started at time T41 before the change (time T42). Thereafter, when the introduction of EGR gas is requested at time T42, the bypass valve 9 is opened (step S64, time T43), the intake passage pressure P1b is reduced, and EGR gas is introduced into the intake passage 3.

  As described above, in the routine of FIG. 12, the EGR valve 12 is opened even when the exhaust passage pressure Pcaft is lower than the intake passage pressure P1b (time T42 in FIG. 13B). As described above, when it is determined that the state of the engine 1 shifts to the EGR introduction operation region, the EGR valve 12 is opened in advance, so that the EGR gas is rapidly introduced into the intake passage 3 when the exhaust passage pressure Pcaft increases. can do.

  The routine of FIG. 14 shows a seventh embodiment of the EGR control routine. The routine of FIG. 14 is repeatedly executed at a predetermined cycle while the engine 1 is operating. In FIG. 14, the same processes as those in FIG. 12 are denoted by the same reference numerals, and the description thereof is omitted.

  In the routine of FIG. 14, the same processing as that of the routine of FIG. 12 is performed until step S62. When it is determined in step S62 that the operating state of the engine 1 shifts to the EGR introduction operation region, the process proceeds to step S71, and the ECU 13 opens the bypass valve 9. Note that the opening degree of the bypass valve 9 at the time of opening the valve may be fully opened, or may be an opening degree that takes into account re-acceleration of the vehicle and introduction of EGR gas. In subsequent step S72, the ECU 13 determines whether or not the exhaust passage pressure Pcaft is higher than the intake passage pressure P1b. When it is determined that the exhaust passage pressure Pcaft is equal to or lower than the intake passage pressure P1b, the process of step S72 is repeatedly executed until the condition of step S72 is affirmed. When the condition of step S72 is affirmed, the process proceeds to step S73, and the ECU 13 opens the EGR valve 12. Thereafter, the current routine is terminated.

  FIGS. 15A to 15D show the time change of the EGR request signal when the routine of FIG. 14 is executed, the time change of the opening degree of the bypass valve 9 and the EGR valve 12, the intake passage pressure P1b and the exhaust passage pressure Pcater. An example of the time change of EGR and the time change of the EGR rate are respectively shown. In FIG. 15B, the line L1 indicates the change in the opening degree of the bypass valve 9, the line L2 indicates the change in the opening degree of the EGR valve 12, the valve opening degree 0 is fully closed, and the valve opening degree 100 is fully open. Respectively. As shown in FIG. 15B, in the routine of FIG. 14, when it is determined that the operating state of the engine 1 shifts to the EGR introduction operating region (affirmative determination in step S62), the EGR request signal is turned on. The bypass valve 9 is opened at time T51 before the change (time T52). As shown in FIG. 15C, the opening of the bypass valve 9 lowers the intake passage pressure P1b and changes the intake passage pressure P1b to be equal to or lower than the exhaust passage pressure Pcater. Thereafter, when the EGR request signal changes to the ON state at time T52, the EGR valve 12 is opened at time T53, and EGR gas is introduced into the intake passage 3.

  As described above, in the routine of FIG. 14, when it is determined that the operation state of the engine 1 shifts to the EGR introduction operation region, the bypass valve 9 is opened in advance before the EGR request signal changes to the ON state, and the intake passage pressure P1b is changed to be equal to or lower than the exhaust passage pressure Pcater. Thus, by changing the intake passage pressure P1b to be equal to or lower than the exhaust passage pressure Pcater, the EGR gas can be rapidly introduced into the intake passage 3 when the EGR valve 12 is opened.

  Each of the EGR control routines shown in FIGS. 2 to 14 may be executed individually or in combination with a plurality of routines. When executed in combination, for example, priorities may be set according to purposes such as improvement of exhaust emission and acceleration of the vehicle, and each routine may be executed based on the priorities.

  The present invention is not limited to the above embodiment, and may be implemented in various forms. For example, the EGR system of the present invention may be applied not only to a diesel engine but also to various internal combustion engines that use gasoline or other fuels. As the bypass valve and the EGR valve, a valve whose opening degree can be adjusted may be provided, or a valve capable of switching between opening and closing may be provided. In such a valve that switches between opening and closing, the flow rate is adjusted by adjusting the period of the valve opening state and the period of the valve closing state.

  The device that is disposed upstream of the compressor of the turbocharger and compresses air to increase the intake pressure is not limited to S / C. For example, an electric compressor driven by an electric motor may be provided in the intake passage upstream of the compressor. The drive source for driving the S / C and the electric compressor is not limited to the electric motor. For example, you may drive these apparatuses using the output of an engine. In this case, the drive shaft of the S / C or electric compressor and the output shaft of the engine are connected via a clutch, and the operation is controlled by this clutch. For example, when the intake pressure is increased, a clutch is connected, and the output of the engine is transmitted to the S / C or the drive shaft of the electric compressor to compress the air. Further, the supercharger that is arranged in the intake passage and constantly supercharges intake air is not limited to the turbocharger. As such a supercharger, a supercharger (S / C) that is always driven to rotate by the crankshaft of the engine, an electric turbocharger (motor assist turbo), or the like may be provided in the intake passage. That is, the present invention is arranged in a second-stage supercharging device that constantly supercharges intake air and an intake passage upstream of the second-stage supercharging device, and supercharges intake air in a predetermined operating state such as during acceleration. The present invention can be applied to an engine having a first stage supercharging device.

  The position of the exhaust passage to which the EGR passage is connected is not limited to the exhaust passage downstream of the exhaust purification catalyst. The EGR passage may be connected to an exhaust passage downstream from the turbine of the turbocharger and upstream from the exhaust purification catalyst.

The figure which shows one form of the diesel engine to which the EGR system of this invention was applied. The flowchart which shows the EGR control routine which ECU of FIG. 1 performs. The flowchart which shows 2nd embodiment of the EGR control routine which ECU of FIG. 1 performs. The figure which shows an EGR gas introduction operation area | region and an EGR gas introduction stop operation area | region. FIGS. 4A and 4B are diagrams illustrating an example of a time change of a physical quantity related to EGR when the routine of FIG. 3 is executed, where FIG. 4A is a time change of a clutch switch, and FIG. 4B is a time change of an opening degree of a bypass valve and an EGR valve. (C) shows the time change of the intake passage pressure and the exhaust passage pressure, and (d) shows the time change of the EGR rate. The flowchart which shows 3rd embodiment of the EGR control routine which ECU of FIG. 1 performs. FIGS. 7A and 7B are diagrams illustrating an example of a time change of a physical quantity related to EGR when the routine of FIG. 6 is executed, where FIG. 7A is a time change of a clutch switch, and FIG. (C) shows the time change of the intake passage pressure and the exhaust passage pressure, and (d) shows the time change of the EGR rate. The flowchart which shows 4th embodiment of the EGR control routine which ECU of FIG. 1 performs. FIGS. 9A and 9B are diagrams illustrating an example of a time change of a physical quantity related to EGR when the routine of FIG. 8 is executed, where FIG. 9A is a time change of a clutch switch, and FIG. (C) shows the time change of the intake passage pressure and the exhaust passage pressure, and (d) shows the time change of the EGR rate. The flowchart which shows 5th embodiment of the EGR control routine which ECU of FIG. 1 performs. FIG. 11 is a diagram illustrating an example of a time change of a physical quantity related to EGR when the routine of FIG. 10 is executed, where (a) shows a time change of the clutch switch, and (b) shows a time change of the opening degree of the bypass valve and the EGR valve. (C) shows the time change of the intake passage pressure and the exhaust passage pressure, and (d) shows the time change of the EGR rate. The flowchart which shows 6th embodiment of the EGR control routine which ECU of FIG. 1 performs. FIG. 13 is a diagram illustrating an example of a time change of a physical quantity related to EGR when the routine of FIG. 12 is executed, where (a) shows a time change of an EGR request signal, and (b) shows an opening time of the bypass valve and the EGR valve. (C) shows the time change of the intake passage pressure and the exhaust passage pressure, and (d) shows the time change of the EGR rate. The flowchart which shows 7th embodiment of the EGR control routine which ECU of FIG. 1 performs. FIG. 15 is a diagram showing an example of a time change of a physical quantity related to EGR when the routine of FIG. 14 is executed, where (a) shows the time change of the EGR request signal, and (b) shows the opening times of the bypass valve and the EGR valve. (C) shows the time change of the intake passage pressure and the exhaust passage pressure, and (d) shows the time change of the EGR rate.

Explanation of symbols

1 Diesel engine (internal combustion engine)
3 Intake passage 4 Exhaust passage 6 Supercharger (Intake pressure adjusting means)
7 Bypass passage 8 Turbocharger (supercharger)
8a Compressor 8b Turbine 9 Bypass valve 10 Exhaust purification catalyst 11 EGR passage 12 EGR valve 13 Engine control unit (EGR control means)

Claims (8)

An EGR system for a supercharged vehicle internal combustion engine, comprising: an EGR passage that connects an exhaust passage and an intake passage upstream of the supercharger; and an EGR valve that adjusts a flow rate of gas flowing through the EGR passage. In
An intake pressure adjusting means that is disposed in an intake passage upstream of the supercharger and compresses air to increase intake pressure, a bypass passage that bypasses the intake pressure adjusting means, and an intake air that flows through the bypass passage A bypass valve for adjusting the flow rate,
The EGR system for a vehicular internal combustion engine with a supercharger, wherein the EGR passage is connected to an intake passage between the intake pressure adjusting means and the supercharger.   When it is determined that acceleration is required for the vehicle and a predetermined EGR gas introduction stop condition for stopping the introduction of EGR gas into the intake passage is satisfied, the bypass valve is closed and the intake valve is closed. The EGR system for an internal combustion engine for a vehicle with a supercharger according to claim 1, further comprising an EGR control means for operating the atmospheric pressure adjusting means.   When acceleration is required for the vehicle in an operating state in which the EGR valve is opened and EGR gas is recirculated to the intake passage, the bypass valve is closed, and then the internal combustion engine is accelerated after the vehicle is accelerated. It is determined whether the operation state of the engine shifts to an EGR gas introduction stop operation region in which the introduction of EGR gas is stopped or an EGR gas introduction operation region in which EGR gas is introduced, and the operation state of the internal combustion engine is determined to be the EGR gas EGR control means is provided that fully closes the EGR valve when it is determined to shift to the introduction stop operation region, and maintains the opening of the EGR valve when it is determined to shift to the EGR introduction operation region. The EGR system of the internal combustion engine for a vehicle with a supercharger according to claim 1.   When the EGR control means determines that the operating state of the internal combustion engine shifts to the EGR gas introduction / stop operation region after the acceleration of the vehicle, the EGR control means, the intake pressure adjusting means, the supercharger, When the intake pressure is high, the EGR valve is closed after a predetermined time, and when the exhaust pressure is high, the EGR valve is immediately closed. The EGR system for an internal combustion engine for a vehicle with a supercharger according to claim 3.   The EGR control means determines that the intake pressure adjusting means and the supercharger are more than the exhaust pressure in the exhaust passage when it is determined that the operating state of the internal combustion engine shifts to the EGR gas introduction stop operation region after the vehicle is accelerated. 4. The EGR valve is closed when it is estimated whether or not the intake pressure in the intake passage between the intake passage and the intake passage is higher, and when the intake pressure is estimated to be higher. 5. EGR system for a vehicle internal combustion engine with a supercharger.   When the vehicle is requested to accelerate in an operating state in which the EGR valve is opened and EGR gas is recirculated into the intake passage, the exhaust pressure in the exhaust passage, the intake pressure adjusting means, and the supercharging EGR that controls the bypass valve so that the pressure difference with the intake pressure of the intake passage between the engine and the engine is maintained at a predetermined value, and the operating state of the internal combustion engine stops the introduction of EGR gas after the vehicle is accelerated. The EGR system for a supercharger-equipped vehicle internal combustion engine according to claim 1, further comprising EGR control means for closing the EGR valve when it is determined to shift to a gas introduction stop operation region.   When it is determined that the intake pressure adjusting means is in an operating state and the operation state of the internal combustion engine shifts from an EGR gas introduction stop operation region in which introduction of EGR gas is stopped to an EGR gas introduction operation region in which EGR gas is introduced. EGR control means is provided that opens the EGR valve to a target opening set after the operating state of the internal combustion engine has shifted to the EGR introduction operation region, and then opens the bypass valve. The EGR system of the internal combustion engine for a vehicle with a supercharger according to claim 1. When it is determined that the intake pressure adjusting means is in an operating state and the operation state of the internal combustion engine shifts from an EGR gas introduction stop operation region in which introduction of EGR gas is stopped to an EGR gas introduction operation region in which EGR gas is introduced. The bypass valve is opened, and then the exhaust pressure in the exhaust passage is compared with the intake pressure in the intake passage between the intake pressure adjusting means and the supercharger, and the exhaust pressure is higher than the intake pressure. The EGR system for an internal combustion engine for a vehicle with a supercharger according to claim 1, further comprising an EGR control means for opening the EGR valve when it is determined.

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