JP4492406B2 - Diesel engine intake / exhaust system - Google Patents

Description

  The present invention relates to an intake / exhaust device for a turbocharged diesel engine.

  Conventionally, in a gasoline engine with a supercharger, in order to prevent surging (surge) generated in the compressor of the supercharger, a bypass provided with a blow-off valve (bypass valve) is provided between the suction side and the discharge side of the compressor. The blowoff valve communicates with the passage and is controlled to open and close.

  The surging is likely to occur when the intake throttle (IT) is suddenly closed to the minimum opening (idle opening) when the engine is operated at a high output. That is, surging occurs when a vehicle whose engine is in a high output state is suddenly decelerated.

  By the way, in the case of a gasoline engine, the output and the intake throttle opening are substantially proportional to keep the air-fuel ratio constant. For this reason, in the gasoline engine, in addition to the deceleration determination, the output determination can be performed based on the intake throttle opening. For example, when the intake throttle is suddenly closed from full open, it is determined that there is a risk of surging due to sudden deceleration from a high output state based on the opening of the intake throttle, and the blow-off valve is opened. It was like that. As described above, in the gasoline engine, the opening / closing of the blow-off valve is controlled based on the intake throttle opening.

  On the other hand, in a diesel engine, a normal intake throttle has not been conventionally provided, and it is not necessary to consider surging due to the intake throttle.

However, in recent years, a throttle valve, that is, an intake throttle may be provided in the intake passage of diesel engines in order to reduce NOx. For example, if you want to earn EGR amount by the EGR gas inlet aperture an intake passage in a diesel engine with an EGR device in a negative pressure state, when it is desired to raise the temperature of the exhaust gas temperature, the intake throttle is provided.

  That is, even in a diesel engine, intake throttling is appropriately performed for the above-described purpose.

  In a diesel engine that performs such intake throttling, there is a high possibility that the operating state of the supercharger enters the surging region (surging occurs), as in the gasoline engine, depending on the output state of the engine.

  Therefore, a diesel engine is known in which a blow-off valve and a bypass passage are provided in order to prevent the occurrence of surging, and the blow-off valve is opened during sudden deceleration to prevent the occurrence of surging (for example, patents). Reference 1).

Japanese Utility Model Publication No. 58-98432 JP-A-8-61073 Japanese Patent Laid-Open No. 10-89079 Japanese Patent No. 3493998

  However, in a diesel engine, the output is not originally controlled by the intake throttle opening. In a diesel engine, basically, it is not necessary to keep the air-fuel ratio constant. Thus, unlike a gasoline engine, the intake throttle opening and the engine output state are not always related to each other. Therefore, in a diesel engine, just because the intake throttle is fully open, the engine is not always in a high output state. Therefore, just because the intake throttle is suddenly closed from almost fully open does not necessarily mean sudden deceleration from the high output state. If the blow-off valve is opened based on the opening of the intake throttle, when there is no possibility of surging, the supercharging pressure is lost and energy is lost. In other words, conventional control based on the intake throttle opening, etc. can prevent surging, but the supercharging pressure is released even when it is not necessary, and the operating efficiency of the turbocharger and thus the diesel engine decreases. There was a problem of doing.

  Accordingly, an object of the present invention is to provide a diesel engine intake / exhaust device that can solve the above-mentioned problems, prevent surging, and improve the operation efficiency of the diesel engine.

In order to achieve the above object, the present invention provides a supercharger having a compressor and a turbine that are respectively disposed in an intake / exhaust passage of an engine, and an intake that is disposed in an intake passage from the compressor to the engine body to throttle intake air. The throttle, a bypass passage communicating the discharge side and the suction side of the compressor, a blow-off valve disposed in the bypass passage, the blow-off valve and the intake throttle are each controlled, and the compressor is decelerated when the vehicle is decelerated. In a diesel engine intake / exhaust device having an engine control unit (ECU) that opens the blow-off valve to prevent the occurrence of surging, a compressor state detecting means for detecting the operating state of the compressor is provided, Compressor status detection The operating conditions of the compressor detected by the means is input to the ECU, the other to the ECU, it may be stored surging risk area which is an area before the pre-operation state of the compressor enters the surging area, the compressor state detecting The means is disposed upstream of the bypass passage between the intake air amount detection means for detecting the intake air amount of the compressor, and the compressor in the intake passage and an intercooler provided downstream of the compressor. The discharge pressure detecting means for detecting the discharge side pressure of the compressor and the compressor in the intake passage and an air cleaner provided at the upstream end of the intake passage are disposed downstream of the bypass passage, And suction pressure detecting means for detecting the suction side pressure of the compressor. U calculates a pressure ratio between the discharge side pressure and the suction side pressure, determines an operating point on the compressor map based on the pressure ratio and the intake air amount, and the operating point is is intended to determine whether the surging danger area, upon deceleration of the vehicle, the ECU is to the operating point on the upper SL compressor map falls on the surging danger area closes the blow-off valve When the operating point on the compressor map enters the surging danger area, the blow-off valve is opened .

  An EGR passage for communicating the exhaust passage and the intake passage, and an EGR valve that opens and closes the EGR passage and is controlled by the ECU, and a barometer upstream of the air cleaner in the intake passage. In addition, an air temperature sensor may be provided, and the ECU may control the intake throttle and the EGR valve to adjust the flow rate of exhaust gas flowing into the engine body from the EGR passage.

  According to the present invention, it is possible to prevent the occurrence of surging and to exhibit an excellent effect that the driving efficiency of the diesel engine can be improved.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The diesel engine intake / exhaust device (hereinafter referred to as intake / exhaust device) of this embodiment is applied to a diesel engine mounted on a vehicle such as a truck, for example.

  As shown in FIG. 1, a diesel engine 1 is arranged in an engine body 2 provided with a combustion chamber, an intake passage 4 and an exhaust passage 5 connected to the engine body 2, and intake and exhaust passages 4 and 5, respectively. A turbocharger 10 having a compressor 8 and a turbine 9, an EGR device 11 for returning a part of exhaust gas to the intake passage 4, and an engine control unit (ECU) 12 are provided.

  In this embodiment, the intake / exhaust device of the diesel engine includes a supercharger 10, an EGR device 11, an ECU 12, an intake throttle (IT) 21 provided in the intake passage 4 for restricting intake air, and the supercharger 10. A bypass passage 22 for communicating the discharge side and the suction side of the compressor 8, a blow-off valve (bypass valve) 24 provided in the bypass passage 22, and an operating state of the compressor 8 of the supercharger 10 are detected. It is comprised from a compressor state detection means, and controls the supercharging pressure of the diesel engine 1.

  The intake passage 4 has a downstream end connected to the engine body 2 and an air cleaner 26 provided at the upstream end. A compressor 8 of the supercharger 10 is disposed between the engine body 2 and the air cleaner 26 in the intake passage 4, and an intercooler 28 that cools the intake air discharged from the compressor 8 is provided downstream of the compressor 8. It is done. An intake throttle 21 is provided at the downstream end of the intake passage 4. The intake throttle 21 is disposed upstream of an inlet 31a of an EGR passage 31 to be described later.

  The exhaust passage 5 has an upstream end connected to the engine main body 2 and a turbine 9 of the supercharger 10 provided at the downstream end. An outlet throttle 29 is provided in the exhaust passage 5 upstream of the turbine 9. The outlet throttle 29 is disposed downstream of the outlet 31b of the EGR passage 31.

  The supercharger 10 includes a turbine 9 that is rotationally driven by exhaust, a compressor 8 that compresses intake air, and a rotary shaft 35 that connects the turbine 9 to the compressor 8. The compressor 8 is driven by the turbine 9 via the rotating shaft 35. The rotation shaft 35 is provided with a turbo tachometer (Rotation sensor) 36 for detecting the number of rotations of the rotation shaft 35. In the present embodiment, the turbo tachometer 36 serves as a turbo rotation speed detection unit that detects the rotation speed of the supercharger 10.

  A bypass passage 22 that connects the suction side and the discharge side of the compressor 8 is connected to the intake passage 4 of the present embodiment. One end of the bypass passage 22 is connected to the intake passage 4 between the compressor 8 and the intercooler 28, and the other end is connected to the intake passage 4 between the compressor 8 and the air cleaner 26. The bypass passage 22 is provided with a blow-off valve 24 that allows the bypass passage 22 to be opened and closed. In the present embodiment, the blow-off valve 24 is driven by a negative pressure actuator 37 having a solenoid valve and connected to a vacuum tank or the like. By operating the blow-off valve 24 to the open side, the suction side and the discharge side of the compressor 8 communicate with each other, and part of the intake air discharged from the compressor 8 passes through the bypass passage 22 and is again sucked into the compressor 8. (The flow is indicated by dotted arrows in FIG. 1).

  The EGR device 11 includes an EGR passage 31 for communicating the intake passage 4 and the exhaust passage 5, an EGR valve (EGR valve, EGRV) 32 for opening and closing the EGR passage 31, and an exhaust for cooling the EGR passage 31. EGR cooler 34 is provided. One end of the EGR passage 31 (on the inlet 31a side) is connected between the engine body 2 and the intake throttle 21 in the intake passage 4, and the other end (outlet 31b side) is connected to the engine body 2 and the outlet throttle in the exhaust passage 5. 29.

  The compressor state detection means of the present embodiment detects an MAF sensor (intake air amount sensor) 41 serving as intake air amount detection means for detecting the intake air amount (MAF) of the compressor 8 and a discharge side pressure P2 of the compressor 8. A discharge pressure sensor 42 serving as a discharge pressure detection unit and a suction pressure sensor 43 serving as a suction pressure detection unit that detects a suction side pressure P1 of the compressor 8 are included. The MAF sensor 41 is disposed upstream of the bypass passage 22 between the air cleaner 26 and the compressor 8 in the intake passage 4. The discharge pressure sensor 42 is disposed upstream of the bypass passage 22 between the compressor 8 and the intercooler 28 in the intake passage 4. The suction pressure sensor 43 is disposed downstream of the bypass passage 22 between the air cleaner 26 and the compressor 8 in the intake passage 4.

  A barometer and an air temperature sensor 46 are provided upstream of the air cleaner 26.

  The engine body 2 is provided with a boost pressure sensor 45 that detects the boost pressure and an engine rotation sensor (not shown) that detects the engine speed.

  Connected to the ECU 12 are a MAF sensor 41, a discharge pressure sensor 42, a suction pressure sensor 43, a turbo tachometer 36, a boost pressure sensor 45, a barometer and air temperature sensor 46, an engine speed sensor, an accelerator opening sensor (not shown), and the like. The signals from these sensors are input. The ECU 12 is connected to the intake throttle 21, the EGR valve 32, the outlet throttle 29, the negative pressure actuator 37, and the like, and drives and controls them. Further, the ECU 12 stores data of a surging danger area described later in advance.

  The intake air introduced through the air cleaner 26 is compressed by the compressor 8, cooled by the intercooler 28, and supplied to the combustion chamber of the engine body 2. The exhaust gas is exhausted through a post-processing device (not shown) after driving the turbine 9 through the exhaust passage 5.

  When the EGR valve 32 is opened, a part of the exhaust gas passing through the exhaust passage 5 flows from the outlet 31b to the EGR passage 31, is cooled in the EGR cooler 34, and then recirculates from the inlet 31a to the intake passage 4. Is done. The recirculated exhaust gas (EGR gas) is supplied to the engine body 2 together with the intake air (fresh air).

  Next, an EGR rate control method performed in this embodiment will be described with reference to FIG.

  In the present embodiment, the EGR rate is indirectly controlled by controlling the intake air amount detected by the MAF sensor 41. The upper graph in FIG. 2 shows the relationship between the intake air amount (MAF) and the EGR rate, and the intake air amount decreases as the EGR rate increases. Therefore, the ECU 12 controls the EGR valve 32 and the intake throttle 21 so as to decrease the intake air amount when increasing the EGR rate, and increase the intake air amount when decreasing the EGR rate. .

  Specifically, the intake air amount (EGR rate) is divided into three regions of a predetermined amount A or more and less than the predetermined amount A to a predetermined amount B or more and less than the predetermined amount B, and different EGR rate control is performed for each region. Do.

  The middle graph in FIG. 2 shows the relationship between the intake air amount and the opening of the intake throttle 21. In the graph, the opening of the intake throttle 21 is closed on the upper side and open on the lower side. The lower graph in FIG. 2 shows the relationship between the intake air amount and the opening degree of the EGR valve 32. In the graph, the opening degree of the EGR valve 32 is opposite to the opening degree of the intake throttle 21, and the upper side is open and the lower side is closed.

  As an example, a case where the intake air amount is reduced from the predetermined amount A to less than the predetermined amount B (increasing the EGR rate) will be described.

  In the region of the predetermined amount A or more, the intake throttle 21 is fully opened and only the EGR valve 32 is operated to the open side. As a result, the EGR gas increases and the intake air amount decreases.

  In a region where the intake air amount is less than the predetermined amount A and greater than or equal to the predetermined amount B, the EGR valve 32 is operated to the open side and the intake throttle 21 is operated to the close side. In this region, the sensitivity of the EGR valve 32 is lower than that in the region of the predetermined amount A or more, and the sensitivity of the intake throttle 21 is not sufficiently high (lower than the region of the predetermined amount B or less). And the intake throttle 21 are cooperatively controlled. As a result, EGR gas increases, fresh air decreases, and the intake air amount further decreases.

  In a region where the intake air amount is less than the predetermined amount B, the EGR valve 32 is fully opened and only the intake throttle 21 is operated to the closed side. This further reduces the intake air amount.

  As described above, the ECU 12 controls the EGR valve 32 and the intake throttle 21, thereby adjusting the ring flow rate of the exhaust gas flowing into the engine body 2 from the EGR passage 31, and the target intake air amount (target EGR rate). ) Is obtained.

  In the present embodiment, the ECU 12 determines a target intake air amount (EGR rate) based on the engine operating state (engine output, engine speed, etc.). Specifically, the intake air amount is determined so as to increase when the engine output is high and decrease when the engine output is low. For this reason, the opening of the intake throttle 21 is basically large when the engine output is high and small when the engine output is low.

  Therefore, when the vehicle is decelerated suddenly from the high engine output state, the intake throttle 21 is suddenly closed and surging occurs.

  Here, as described above, the intake throttle 21 is not always in the high engine output state, but is always fully opened when the intake air amount is equal to or greater than the predetermined amount A. Therefore, as in the gasoline engine described in the “Background Art” section, when trying to determine the occurrence of surging based on the opening of the intake throttle, even when the vehicle is suddenly decelerated from a state where the engine is not in a high output state, Judging that there is a possibility of surging, the blow-off valve is unnecessarily opened and the operation efficiency of the compressor is lowered.

  Therefore, the intake / exhaust device of the present embodiment performs the following supercharging pressure control in order to prevent a decrease in the operating efficiency of the compressor 8 regardless of the opening of the intake throttle 24.

  A program for executing the supercharging pressure control will be described with reference to the flowchart of FIG. The program is stored in advance in the ECU 12 and is appropriately executed by the ECU 12.

  Step S0 is a start, for example, when the diesel engine 1 is started.

  In step S1, the accelerator opening APS detected by the accelerator opening sensor, the engine speed Ne detected by the engine speed sensor, and the fuel injection amount determined based on the accelerator opening APS and the engine speed Ne. Q is read into the ECU 12.

  In step S2, the ECU 12 determines whether or not the vehicle is in a deceleration state based on the accelerator opening APS, the engine speed Ne, and the fuel injection amount Q.

  If it is determined in step S2 that the vehicle is decelerating, the process proceeds to step S3. On the other hand, if it is determined that the vehicle is not in a deceleration state, the process returns to step S1.

  In step S3, the intake air amount (MAF) detected by the MAF sensor 41, the discharge side pressure P2 detected by the discharge pressure sensor 42, and the suction side pressure P1 detected by the suction pressure sensor 43 are sent to the ECU 12. Is read. Further, the ECU 12 calculates a pressure ratio P2 / P1 from the discharge side pressure P2 and the suction side pressure P1.

  In step S4, the ECU 12 determines (determines) whether or not the operating state of the compressor 8 is in the surging danger region. In the present embodiment, the ECU 12 determines an operating point on the compressor map based on the pressure ratio P2 / P1 and the intake air amount, and determines whether or not the operating point is in a surging danger region. Specifically, the function F (MAF, P2 / P1) is stored in the ECU 12 in advance, and the ECU 12 determines from the function F (MAF, P2 / P1), the intake air amount, and the pressure ratio P2 / P1. The function F (MAF, P2 / P1) is defined based on, for example, a surging danger line C2 on the compressor map of FIG. 4 to be described later. If C2 (MAF) <= P2 / P1, it is within the surging danger area, and C2 If (MAF)> P2 / P1, the function is outside the surging risk area.

  If it is determined in step S4 that the operating state of the compressor 8 is in the surging danger region, the process proceeds to step S5. On the other hand, if it is determined in step S4 that it is not in the surging danger area, the process returns to step S1.

  In step S5, the ECU 12 operates the blow-off valve 24 to the open side.

  Step S6 is a return, for example, returning to step 0 (start) again.

  Next, based on FIG. 4 to FIG. 6, the determination of the compressor operation state performed in step 4 and the opening operation with the blow-off valve 24 performed in step 5 will be described in more detail.

  4 and 5 are compressor maps showing the performance characteristics of the compressor 8. The vertical axis represents the pressure ratio P2 / P1 between the discharge side pressure P2 and the suction side pressure P1 of the compressor 8, and the horizontal axis represents the intake air amount ( MAF). On the compressor map, the operating state of the compressor 8 is uniquely determined as an operating point on the map by the intake air amount (MAF) read in step S3 and the pressure ratio (P2 / P1) calculated in step S3. It is determined.

  The surging line C1 in FIG. 4 and FIG. 5 is a line that defines the surging limit of the compressor 8. When the operating point of the compressor 8 enters the surging region (shaded portion) on the left side of the surging line C1, surging is performed. appear. The surging danger line C2 is appropriately (arbitrarily) set for each compressor 8 in consideration of the responsiveness of the blow-off valve 24 based on the surging line C1, and is a diagonal line between the surging danger line C1 and the surging danger line C2. Is set as a surging danger region that is a region (pre-surge region) before the operating point (operating state) of the compressor 8 enters the surging region. Based on this surging danger line C2, a function F (MAF, P2 / P1) in step S4 is defined. The right side of the surging danger line C2 is a stable operation region.

  First, an example of operating the blow-off valve 24 to the open side in order to prevent surging will be described with reference to FIGS.

  FIG. 6 shows the accelerator opening (APS), intake air amount (MAF), EGR valve opening and intake throttle opening (EGRV and ITV), boost pressure (Boost), and pressure ratio (P2 / P1) in order from the top. It is a time chart.

  At time t0, the blow-off valve 24 is closed, and the engine 1 is operated at a high output (the accelerator opening APS is fully opened). At this time, the operating point of the compressor 8 is at a position indicated by D1 in FIG.

  If the vehicle is suddenly decelerated at time t1 (accelerator opening APS is fully closed) and the fuel injection amount (Qfin) is rapidly reduced to a predetermined idle injection amount, the engine output is drastically and greatly reduced. . As the engine output decreases, the target intake air amount (target MAF) is determined to be a low value, and the ECU 12 operates the EGR valve 32 to the open side. When the actual intake air amount (actual MAF) decreases to a predetermined value (predetermined value A in FIG. 2) at time t2, the ECU 12 operates the intake throttle 21 to the closed side.

  As a result, the actual intake air amount decreases and the compressor discharge-side pressure P2 increases. This means that the operating point shifts to the upper left on the compressor map of FIG. That is, the operating state of the compressor 8 approaches the surging danger area.

  When the operating point of the compressor 8 is located on the surging danger line C2 at time t3 (indicated by D2 in FIG. 5), the ECU 12 determines that the operating state of the compressor 8 has entered the surging danger area, and the blow-off valve 24 is turned on. It operates on the open side (in this embodiment, it is fully open). As a result, part of the intake air discharged from the compressor 8 returns to the suction side of the compressor 8, and the discharge side pressure P2 rapidly decreases. On the other hand, a part of the intake air circulates in the compressor 8 to reduce the intake air amount (the EGR rate is increased). This means that the operating point shifts from D2 to the lower left side on the compressor map of FIG.

  As a result of the decrease in the discharge side pressure P2, the state of the compressor 8 deviates from the surging danger area. In the present embodiment, even after the state of the compressor 8 deviates from the surging danger region, until the operating point of the compressor 8 (intake air amount and pressure ratio P2 / P1) reaches a predetermined value (D3) (for example, supercharging The blow-off valve 24 is opened until the number of revolutions of the machine 10 does not decrease. Thereafter, the blow-off valve 24 is closed.

  Next, the case where the blow-off valve 24 is held closed even when the vehicle is decelerated will be described with reference to FIGS. 4 and 5. Here, as an example, a case where the vehicle is decelerated from the engine middle load state will be described.

  When the engine is in a medium load state, the operating point of the engine is located at d1 on the stable operation region side of the operating point D1 in the high load (high output) state.

  When the intake throttle 21 is actuated to the closed side, the intake air amount decreases and the compressor discharge side pressure P2 increases as described above, and the operating point in FIG. 5 shifts from d1 to d2. However, since the operation point d1 before the intake throttle operation is located on the stable operation region side from D1, the operation point of the compressor 8 does not enter the surging risk region even at the operation point d2. That is, in this case, although the deceleration determination is made in step S2 of FIG. 3, in step S4, the ECU 12 determines that the operating state of the compressor 8 is not in the surging danger region, and the ECU 12 keeps the blow-off valve 24 closed. Hold.

  As described above, in this embodiment, when the pressure sensor 42, 43 attached to the diesel engine 1 and the intake air amount sensor 41 are used, the operating state (region) of the compressor 8 becomes a surging danger region (surging). When approaching the region, the blow-off valve 24 is opened electrically (ie, controlled by the ECU 12) before surging occurs. On the other hand, when the operating state of the compressor 8 does not become a surging danger region, the boost pressure is not lowered by holding the blow-off valve 24 closed regardless of the opening of the intake throttle 21.

  In the present embodiment, the blow-off valve 24 can be controlled in accordance with the actual state (situation) of the supercharger 10 using the compressor map of the actual supercharger 10. Thus, surging of the supercharger 10 can be prevented without losing supercharging pressure wastefully, and damage to the supercharger 10 and the intake passage 4 and noise generation can be reliably prevented, and The operating efficiency of the supercharger 10 and the diesel engine 1 can be improved.

  The intake / exhaust device of the present embodiment does not simply open the blow-off valve by making a deceleration determination in a diesel engine in which an intake throttle is provided and a problem of surging occurs. That is, conventionally, the accelerator opening, the throttle opening, or the pressure on the compressor discharge side is simply detected, and the blow-off valve is opened when the sudden deceleration is determined from the detected value. Therefore, even when the compressor is not actually in the surging danger area, the blow-off valve is opened, resulting in energy loss. In the present embodiment, it is possible to accurately grasp the operation state of the compressor 8 by determining whether or not the operation state of the compressor 8 is in the surging danger region by the compressor state detection means, and the intake throttle 21 is throttled. If there is no fear of occurrence of surging, the blow-off valve 24 is not opened unnecessarily, the surging of the compressor 8 is prevented and the diesel engine 1 is protected, and the operation efficiency of the compressor 8 and the diesel engine 1 is improved. ing.

Next, a reference embodiment will be described based on FIG.

The diesel engine intake / exhaust device of the reference embodiment is different from the diesel engine intake / exhaust device of the above-described embodiment only in the configuration of the compressor state detection means, and the other is the same.

  On the compressor maps of FIGS. 4 and 5, the operating state of the compressor 8 is unambiguous as an operating point on the map also by the intake air amount (MAF) and the turbo rotational speed (shown by the dotted line in FIGS. 4 and 5). To be determined.

Therefore, in the reference embodiment, the compressor state detection means is constituted by the MAF sensor 41 and the turbo tachometer 36, and the ECU 12 operates on the compressor map based on the intake air amount and the rotational speed of the supercharger 10. And determine whether or not the operating point is in the surging danger region.

A program for executing the supercharging pressure control in the reference mode will be described with reference to the flowchart of FIG. The flowchart of FIG. 7 differs from the flowchart of FIG. 3 in steps S3 and S4, and is otherwise the same. Only step S3 and step S4 will be described below.

  In step S3, the intake air amount (MAF) and the rotation speed (Nturbo) of the supercharger 10 (rotary shaft 32) are read.

  In step S4, the ECU 12 determines that the operating state (operating point) of the compressor 8 is a surging risk based on the function F (MAF, Nturbo) stored in the ECU 12, the intake air amount, and the rotational speed Nturbo of the supercharger 10. It is determined (determined) whether it is in the area.

  Further, similarly to the above-described embodiment, when it is determined in step S4 that the operating state of the compressor 8 is in the surging danger region, step S5 is executed. On the other hand, if it is determined in step S4 that it is not in the surging danger area, the process returns to step S1.

In the reference form, the same effect as in the above-described embodiment can be obtained.

  In addition, this invention is not limited to the above-mentioned embodiment, Various modifications and application examples can be considered.

  For example, in this embodiment, when the operating state of the compressor 8 enters the surging danger region, the blow-off valve 24 is operated to the open side until it is fully opened. However, the present invention is not limited to this, and the opening degree of the blow-off valve 24 is set to the compressor. It can be considered that the control is performed more finely according to the operation state of No. 8.

  Further, the intake / exhaust device of the present invention is applied to an engine that employs a premixed combustion system in which fuel is injected before the compression top dead center of the piston and the fuel mixture is ignited after a predetermined premixing period. It is conceivable to provide. The premixed combustion type engine requires a larger amount of EGR than the conventional combustion type, and the intake air amount will be further reduced in order to obtain the EGR amount. By providing this, it is possible to improve the driving efficiency while preventing the occurrence of surging.

1 shows an intake / exhaust device for a diesel engine according to an embodiment of the present invention. It is a figure for demonstrating the EGR rate control performed in this embodiment. It is a flowchart for the supercharging pressure control of this embodiment. It is a compressor map which shows the operation state of the compressor of this embodiment. It is a compressor map which shows the operation state of the compressor of this embodiment. It is a time chart of the diesel engine and intake / exhaust apparatus of this embodiment. It is a flowchart for the supercharging pressure control of a reference form.

Explanation of symbols

1 Diesel Engine 4 Intake Passage 5 Exhaust Passage 8 Compressor 9 Turbine 10 Supercharger 12 Engine Control Unit (ECU)
21 Intake throttle 22 Bypass passage 24 Blow-off valve 41, 42, 43 Compressor state detection means

Claims (2)

A turbocharger having a compressor and a turbine respectively disposed in an intake / exhaust passage of the engine; an intake throttle disposed in an intake passage extending from the compressor to the engine main body to throttle intake air; and a discharge side and an intake side of the compressor; A bypass passage communicating with each other, a blow-off valve disposed in the bypass passage, the blow-off valve and the intake throttle are controlled, and the blow-off valve is opened to prevent the compressor from surging when the vehicle is decelerated. In a diesel engine intake / exhaust device comprising an engine control unit (ECU) as described above,
Compressor state detecting means for detecting the compressor operating state is provided, and the compressor operating state detected by the compressor state detecting means is input to the ECU, and the compressor operating state is previously set in the surging region. Store the surging danger area that is the area before entering,
The compressor state detection means includes an intake air amount detection means for detecting an intake air amount of the compressor, and the compressor in the intake passage and an intercooler provided downstream of the compressor than the bypass passage. Disposed downstream of the bypass passage between the discharge pressure detecting means disposed upstream and detecting the discharge side pressure of the compressor and the air cleaner provided at the upstream end of the intake passage and the compressor in the intake passage And an intake pressure detecting means for detecting the suction side pressure of the compressor, and the ECU calculates a pressure ratio between the discharge side pressure and the suction side pressure, and calculates the pressure ratio and the intake air. And determine the operating point on the compressor map based on the Is intended to determine Luke,
During deceleration of the vehicle, the ECU is, until the operating point on the upper SL compressor map falls on the surging danger region, and hold closed the blow-off valve, the operating point on the compressor map the An intake / exhaust device for a diesel engine, wherein the blow-off valve is opened when entering a surging danger region . An EGR passage for communicating the exhaust passage and the intake passage, and an EGR valve that opens and closes the EGR passage and is controlled by the ECU;
The diesel engine intake / exhaust device according to claim 1 , wherein the ECU controls the intake throttle and the EGR valve to adjust a recirculation flow rate of exhaust gas flowing into the engine body from the EGR passage .

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