JP2007291961A - Control device of internal combustion engine with centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely avoid surge during the acceleration while well securing a re-acceleration performance after avoiding the surge in a control device of an internal combustion engine with a centrifugal compressor. <P>SOLUTION: This control device comprises a variable nozzle turbosupercharger with an electric motor 32. When it is determined that surge occurs in the compressor 30a of the turbosupercharger 30, the VN opening of a variable nozzle 30c is controlled to an open side for avoiding the surge. The rotation of the compressor 30a is so assisted by the electric motor 32 that the rotational speed of a turbosupercharger after the VN opening of the variable nozzle 30c is controlled can maintain the actual rotational speed immediately before the determination of the surge. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine including a centrifugal compressor.

  Conventionally, for example, Patent Document 1 discloses a control device for an internal combustion engine including a variable nozzle turbocharger. In this conventional control device, when a surge occurs in the compressor (centrifugal compressor) of the turbocharger, the opening degree of the variable nozzle is controlled to be more open than normal in order to avoid the surge. I have to.

JP-A-2005-240756 Japanese Patent Laying-Open No. 2005-201092 JP 2005-69178 A JP-A-4-164135

  According to the above-described conventional control device for an internal combustion engine, when the surge occurs, the rotational speed of the turbine can be reduced by controlling the opening degree of the variable nozzle to be more open than the normal time. The pressure ratio before and after can be lowered. For this reason, a surge can be avoided. However, opening the variable nozzle more leads to a reduction in the amount of air supplied to the internal combustion engine. For this reason, when a surge occurs during acceleration of the internal combustion engine, if the opening of the variable nozzle that is opened to avoid the surge is excessive, the reacceleration performance of the internal combustion engine after the surge avoidance is deteriorated. The conventional control device described above is not intended for surge countermeasures during acceleration, and still leaves room for investigation in constructing control that takes into account re-acceleration performance after surge avoidance.

  The present invention has been made to solve the above-described problems. A centrifugal compressor capable of reliably avoiding a surge during acceleration while ensuring good reacceleration performance after avoiding a surge is provided. An object of the present invention is to provide a control device for an internal combustion engine.

A first invention is a control device for an internal combustion engine provided with a centrifugal compressor in an intake passage,
Surge determining means for determining whether or not a surge has occurred in the centrifugal compressor;
When the surge determination means determines that a surge has occurred, the boost pressure or compressor speed is controlled to avoid the surge, and the boost pressure or compressor speed is controlled. As a result, a supercharging state control means for causing a reduction in exhaust pressure of the internal combustion engine or a reduction in the amount of intake air to the internal combustion engine,
When the supercharging pressure or the compressor speed is controlled by the supercharging state control means, assists the rotation of the centrifugal compressor so that the supercharging pressure or the compressor speed before the surge determination is maintained. An assist mechanism to
It is characterized by providing.

The second invention is the first invention, wherein the centrifugal compressor is configured as a compressor of a turbocharger with an electric motor,
The assist mechanism is the electric motor.

  In addition, according to a third invention, in the first or second invention, the control amount of the supercharging pressure or the compressor rotational speed by the supercharging state control means is the supercharging pressure or the compressor rotational speed before surge determination. It is the minimum amount to maintain.

  In a fourth aspect based on any one of the first to third aspects, the supercharging state control means controls the supercharging pressure or the compressor rotational speed in accordance with an operating region of the centrifugal compressor. The speed is variable.

The fifth invention further comprises surge level determining means for determining the magnitude of surge in any of the first to fourth inventions,
The control speed of the supercharging pressure or the compressor speed is made variable according to the magnitude of the determined surge.

According to the first invention, when the supercharging state control means is a means for reducing the exhaust pressure of the internal combustion engine as a result of controlling the supercharging pressure or the compressor speed for avoiding a surge. When assisting by the assist mechanism, the amount of intake air to the internal combustion engine can be increased compared to the state before the judgment of the surge due to the influence of the decrease in exhaust pressure, and accordingly, the centrifugal compressor The amount of air passing through can be increased. For this reason, it is possible to control the internal combustion engine to the state of the supercharging pressure or the compressor rotation speed before the surge determination while avoiding the surge. Further, when the supercharging state control means is a means for causing a reduction in the amount of intake air to the internal combustion engine as a result of performing the above-described control for avoiding the surge, the assist mechanism is used to assist, The reduced intake air amount due to the influence of surge avoidance by the supply state control means can be compensated. For this reason, in this case as well, it is possible to control the internal combustion engine to the state of the supercharging pressure or the compressor rotational speed before the surge determination while avoiding the surge.
For this reason, according to this invention, the surge at the time of acceleration can be avoided reliably, ensuring the re-acceleration performance after surge avoidance favorably.

  According to the second invention, using the electric motor of the turbocharger with electric motor as an assist mechanism, it is possible to reliably avoid a surge during acceleration while ensuring good reacceleration performance after avoiding the surge.

  According to the third aspect of the invention, it is possible to suppress the occurrence of large torque fluctuations in the internal combustion engine in order to avoid surge.

  According to the fourth aspect of the invention, it is possible to avoid a surge while satisfactorily suppressing an abrupt change in the operating state of the internal combustion engine and a torque fluctuation resulting therefrom.

  According to the fifth invention, regardless of the magnitude of the detected surge, the control amount of the supercharging state control means required to avoid the surge can be quickly controlled, and the occurrence of the surge The torque fluctuation of the internal combustion engine due to can be suppressed satisfactorily.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a schematic configuration diagram for explaining the configuration of the first embodiment of the present invention. The system shown in FIG. 1 includes a diesel engine 10 having a plurality of cylinders (four cylinders in FIG. 1), a fuel supply system that supplies fuel to the diesel engine 10, an intake system that supplies air to the diesel engine 10, An exhaust system that exhausts exhaust gas from the diesel engine 10 and a control system that controls the operation of the diesel engine 10 are provided.

  The fuel supply system of the diesel engine 10 is provided with a fuel injection valve 12 for directly injecting fuel into the combustion chamber. Fuel stored in a fuel tank (not shown) is pumped up by the fuel pump 14, compressed to a predetermined fuel pressure, and supplied to the fuel injection valve 12.

  The intake system of the diesel engine 10 includes an intake manifold 16 and an intake pipe (intake passage) 18 connected to the intake manifold 16. Air is taken into the intake pipe 18 from the atmosphere and distributed to the combustion chambers of the respective cylinders via the intake manifold 16. An air cleaner 20 is attached to the inlet of the intake pipe 18. An air flow meter 22 that outputs a signal corresponding to the flow rate of air sucked into the intake pipe 18 is provided in the vicinity of the downstream side of the air cleaner 20. Further, an intake pressure sensor 23 for detecting an inlet air pressure of a compressor 30a, which will be described later, is disposed downstream of the air flow meter 22.

  A throttle valve 24 is provided upstream of the intake manifold 16. An intercooler 26 that cools the compressed air is provided upstream of the throttle valve 24. A supercharging pressure sensor 28 that outputs a signal corresponding to the pressure in the intake manifold 16 is disposed downstream of the throttle valve 24.

  A compressor (centrifugal compressor) 30 a of a variable nozzle type turbocharger 30 is provided in the middle of the intake pipe 18 from the air flow meter 22 to the throttle valve 24. The turbocharger 30 includes a compressor 30a, a turbine 30b, and a variable nozzle 30c. The compressor 30a and the turbine 30b are integrally connected by a connecting shaft, and the compressor 30a is rotationally driven by the exhaust energy of the exhaust gas input to the turbine 30b.

  The variable nozzle 30c can be opened and closed by an actuator (not shown). When the opening of the variable nozzle 30c (hereinafter referred to as “VN opening”) is reduced, the inlet area of the turbine 30b is reduced, and the flow rate of the exhaust gas blown to the turbine 30b can be increased. As a result, the rotational speeds of the compressor 30a and the turbine 30b (hereinafter referred to as “turbo rotational speed”) are increased, so that the supercharging pressure can be increased. Conversely, when the opening of the variable nozzle 30c is increased, the inlet area of the turbine 30b is increased, and the flow rate of the exhaust gas blown to the turbine 30b is decreased. As a result, the turbo rotation speed decreases, so that the supercharging pressure can be reduced.

  An electric motor 32 is disposed between the compressor 30a and the turbine 30b. A connecting shaft between the compressor 30 a and the turbine 30 b is also a rotor of the electric motor 32. That is, the compressor 30a and the turbine 30b and the rotor of the electric motor 32 rotate as a unit. Therefore, the compressor 30a can be forcibly driven by operating the electric motor 32. A turbo rotation speed sensor 34 that outputs a signal corresponding to the turbo rotation speed is attached to the connecting shaft of the turbocharger 30.

  The exhaust system of the diesel engine 10 includes an exhaust manifold 36 and an exhaust pipe 38 connected to the exhaust manifold 36. The exhaust gas discharged from each cylinder of the diesel engine 10 is collected in the exhaust manifold 36 and is discharged to the exhaust pipe 38 via the exhaust manifold 36. In addition, the system shown in FIG. 1 includes an exhaust gas recirculation passage 40 that communicates the intake pipe 18 and the exhaust pipe 38. An EGR valve 42 is provided in the middle of the exhaust gas recirculation passage 40.

  The control system of the diesel engine 10 includes an ECU (Electronic Control Unit) 50 and a motor controller 52. The motor controller 52 controls the energization state of the electric motor 32 based on a command from the ECU 50. Electric power to the electric motor 32 is supplied from the battery 54. The ECU 50 is a control device that comprehensively controls the entire system. In addition to the motor controller 52, various actuators such as the fuel injection valve 12, the throttle valve 24, the variable nozzle 30 c, and the EGR valve 42 are connected to the output side of the ECU 50. Further, on the input side of the ECU 50, in addition to the air flow meter 22, the supercharging pressure sensor 28, and the turbo speed sensor 34, an accelerator opening sensor 56 for detecting the accelerator opening, a throttle for detecting the throttle opening. Various sensors such as an opening sensor 58 and a crank angle sensor 60 for detecting the engine speed NE are connected. In addition to these devices and sensors, a plurality of devices and sensors are connected to the ECU 50, but the description thereof is omitted here. The ECU 50 drives each device according to a predetermined control program based on the output of each sensor.

  In the system of the present embodiment configured as described above, the ECU 50 stores a map (not shown) that defines the relationship between the operating state of the diesel engine 10 and the target turbo speed under the operating state. is doing. Then, the ECU 50 performs feedback control of the turbo rotational speed so that the actual turbo rotational speed detected by the turbo rotational speed sensor 34 matches the target turbo rotational speed corresponding to the current operating state. That is, the ECU 50 calculates the turbo speed deviation between the target turbo speed and the actual turbo speed, and controls the VN opening and the assist amount of the electric motor 32 so that the turbo speed deviation becomes zero.

[Surge detection method]
Next, a surge determination method for the compressor 30a will be described.
FIG. 2 is a diagram showing the relationship between the pressure ratio P3 / P0 before and after the compressor 30a and the passing air amount Ga of the compressor 30a. A curve indicated by a bold line in FIG. 2 represents a surge line. In FIG. 2, a hatched area on the left side of the surge line corresponds to the surge area. That is, the surge is likely to occur under a situation where the pressure ratio P3 / P0 of the compressor 30a is large and the passing air amount Ga is small. Specifically, a surge may occur, for example, during acceleration when the throttle opening is fully opened.

  FIG. 3 is a diagram for explaining the surge determination method of the present embodiment. More specifically, FIG. 3A is an enlarged view of the pulsation of the compressor passing air amount Ga caused by the surge of the compressor 30a, and FIG. 3B is a surge detection. It is a figure for demonstrating the specific process for.

  In the surge determination method of this embodiment, based on the second-order differential value of the compressor passing air amount Ga, the inflection point of the pulsation of the compressor passing air amount Ga as shown in FIG. 3A (in FIG. 3A). When a large change is recognized in the compressor passing air amount Ga before and after the inflection point, a surge is determined.

More specifically, as shown in FIG. 3 (B), the measured value (the plotted point in FIG. 3 (B)) of the current compressor passing air amount Ga and the previous corresponding value at every predetermined sampling time of the ECU 50. The difference from the measured value of the air amount Ga (that is, the first-order differential value (∂Ga / ∂t) of the compressor passing air amount Ga with time is calculated. Then, the calculated first-order differential value and the previous one are calculated. A difference from the second-order differential value (that is, a second-order differential value (∂ ² Ga / ∂t ² ) is calculated. Then, when the calculated second-order differential value is equal to or greater than a predetermined value, a surge is determined.

  The sign of the first-order differential value is reversed before and after the inflection point where the compressor passing air amount Ga changes from increase to decrease or before and after the inflection point where the air amount Ga changes from decrease to increase. For this reason, at the time of the inversion, the value of the second-order differential value that is the difference between the first-order differential values becomes large. On the other hand, when the compressor passing air amount Ga is monotonously increasing or decreasing, even if the first-order differential value is greatly calculated because the change in the air amount Ga is large. The second-order differential value, which is the difference between, is not as large as that at the time of inversion.

  As described above, according to the surge determination method of the present embodiment using the second order differential value, it is possible to accurately detect that there is a large change in the compressor passing air amount Ga before and after the inflection point of the pulsation. This makes it possible to detect the surge early and reliably regardless of the magnitude of the surge (pulsation). Here, the surge determination is performed when the second-order differential value of the passing air amount Ga of the compressor 30a becomes a predetermined value or more. However, the second-order differential value calculation target in the surge determination method described above is used. However, the present invention is not limited to this, and any parameter that changes due to the operation of the centrifugal compressor 30a may be used. Specifically, the compressor inlet air pressure or the compressor inlet air temperature may be used. .

[Features of Embodiment 1]
If a surge has occurred during acceleration, the pressure ratio P3 / P0 of the compressor 30a can be lowered by opening the opening (VN opening) of the variable nozzle 30c, and the surge can be avoided. . However, when the VN opening is further opened, the amount of exhaust energy recovered in the turbine 30b is reduced, so that the supercharging pressure is lowered. As a result, the amount of air Ga supplied to the diesel engine 10 decreases. Therefore, if it is left as it is, the driver is given a feeling of deceleration during acceleration.

  Therefore, the system of the present embodiment aims to avoid a surge without adversely affecting the drivability of the diesel engine 10 during acceleration, that is, without deteriorating the reacceleration performance after avoiding the surge. did. For this purpose, when a surge is detected, the VN opening is controlled to the open side and the assist amount of the motor 32 is increased (including the case where the motor 32 is moved from the non-driving state to the driving state). The actual turbo speed immediately before the surge judgment (detection) is maintained.

Next, specific processing in the first embodiment will be described with reference to FIGS. 4 and 5.
FIG. 4 is a flowchart of a routine executed by the ECU 50 in the first embodiment to realize the above function. In the routine shown in FIG. 4, first, predetermined processing is performed on signals input from the various sensors described above (step 100). By this input signal processing, various parameters representing the operating state of the diesel engine 10 are acquired. Specifically, the engine speed NE, accelerator opening, target throttle opening, fuel injection amount, actual boost pressure, actual turbo speed, and the like are acquired.

  Next, it is determined whether or not a condition for starting and continuing the assist by the electric motor 32 is satisfied (step 102). Specifically, these conditions are the following two points. The first point is whether or not there is a need for electric assist, for example, whether or not the diesel engine 10 is in a low rotation high load region or a transient state (acceleration state). The second point is whether there is no condition for prohibiting the electric assist, for example, whether the remaining battery level is sufficient, or whether the turbo rotation speed is lower than the assist allowable value. When this electric assist start / continuation condition is not satisfied, the processing of this routine is terminated as it is.

  If the electric assist start / continuation condition is satisfied, next, a process for determining the target turbo speed is performed (step 104). The target turbo speed is predetermined by a map in relation to the accelerator opening, the engine speed NE, and the target throttle opening. Here, the target turbo speed according to the current operating state is determined by referring to the map.

  Next, the VN opening is fixed to the base VN opening according to the map shown in FIG. 5 (step 106). FIG. 5 is a diagram showing a map that defines the base VN opening degree. In FIG. 5, the maximum opening (fully opened) is represented as 0% and the minimum opening is represented as 100%. The higher the rotation speed and load, the higher the exhaust pressure, so the variable nozzle needs to be opened. For this reason, the base VN opening degree map is determined so that the opening degree increases as the engine speed NE increases. The base VN opening map moves to the open side (lower side in FIG. 5) as the engine load increases, and moves to the closed side (upper side in FIG. 5) as the engine load decreases. In this step 106, the base VN opening according to the current operating state is determined according to the base VN opening map as shown in FIG. 5, and the actual VN opening is controlled to be the base VN opening. . The base VN opening is determined according to the engine speed NE and the engine load. In this system, the magnitude of the engine load is determined from the accelerator opening, the target throttle opening, the fuel injection amount, or the like.

  After the VN opening is set to the base VN opening, power supply to the motor 32 is started and turbo rotation assist is started in order to quickly increase the actual turbo speed to the target turbo speed. (Step 108).

  Next, it is determined whether or not the surge determination flag is ON (step 110). The ECU 50 determines whether or not a surge has occurred using the surge determination method described above, and turns on the surge determination flag when determining that a surge has occurred.

  If it is determined in step 100 that the surge determination flag is ON, the target turbo speed is fixed to the actual turbo speed immediately before the surge determination (step 112). More specifically, the ECU 50 stores the actual turbo speed for each predetermined sampling time, and in this step 112, the actual turbo speed at a time several milliseconds before the time when the surge determination flag is turned on. Fixed to a number.

  Next, the VN opening is controlled so as to be the opening that can maintain the actual turbo speed immediately before the surge determination and that is the most closed position (step 114). There is a certain range in the VN opening for maintaining the same actual turbo speed. Here, the most closed VN opening that can avoid a surge is selected from the width. Next, the assist amount of the electric motor 32 is increased so that the actual turbo speed immediately before the surge determination is maintained (step 116).

  Next, it is determined whether or not the surge determination flag has been turned OFF because the surge has been avoided (step 118). As a result, if the surge has not been avoided, the VN opening is further opened by a predetermined amount (step 120), and the electric assist amount is further increased (step 122).

  If it is determined in step 118 that the surge determination flag has been turned OFF, whether or not the amount of change in the engine speed NE and the amount of change in the intake air amount Ga have become larger than the respective predetermined determination values. A determination is made (step 124). If the determination in step 124 is satisfied, that is, if a change of several percent is recognized in the amount of change in the engine speed NE or the intake air amount Ga, it can be determined that the vehicle is sufficiently away from the surge region.

  Therefore, in this case, the target turbo speed fixed in step 112 is gradually shifted to a value determined in relation to the operation state of the diesel engine 10 (step 126). Further, when it is determined in step 110 that the surge determination flag is not ON, the process of step 126 is also executed.

  Next, it is determined whether or not an electric assist stop condition is satisfied (step 128). If the turbo rotational speed deviation is still larger than the predetermined determination value, it is determined that the electric assist stop condition is not satisfied. In this case, the electric assist is continued as it is. On the other hand, when the turbo rotational speed deviation becomes smaller than the determination value, it is determined that the electric assist stop condition is satisfied.

  When it is determined that the electric assist stop condition is satisfied, assist stop control is performed (step 130). When the assist stop control is finished and there is no electric assist, feedback control of the VN opening is then started so that the current actual turbo speed becomes the target turbo speed based on the operating state ( Step 132).

  According to the routine shown in FIG. 4 described above, when it is determined that a surge has occurred, the output of the diesel engine 10 can be maintained immediately before the surge determination. Specifically, when a surge determination is made, the exhaust pressure of the diesel engine 10 can be reduced by controlling the VN opening to the open side. Then, the turbo rotational speed, which decreases as the VN opening degree is controlled to the open side, is maintained by the assist of the electric motor 32 so that the actual turbo rotational speed immediately before the surge determination is maintained. Since the exhaust pressure is reduced, the air amount Ga supplied to the diesel engine 10 can be increased when the motor 32 maintains the actual turbo speed at the actual turbo speed immediately before the surge determination. As this air amount Ga increases, the amount of air passing through the compressor also increases, so that surge can be avoided while maintaining the actual turbo speed high.

  Thus, according to the above method, a surge can be avoided without causing a decrease in torque, and the actual turbo rotation speed can be judged while the surge is being avoided since the judgment of the surge. Can be controlled by the previous value. For this reason, it is possible to avoid the occurrence of torque fluctuation during the execution of surge avoidance so as not to give the driver a feeling of deceleration. Moreover, the reacceleration performance after surge avoidance can be ensured satisfactorily.

  Further, according to the processing of the above routine, the VN opening is controlled so as to be the opening that can maintain the actual turbo rotation speed immediately before the surge determination and is the most closed opening. For this reason, the control amount of the VN opening degree for avoiding the surge can be minimized to suppress the occurrence of large torque fluctuations in the diesel engine 10 for avoiding the surge.

  Further, according to the system of this embodiment, in order to avoid a surge, it is not necessary to separately provide a bypass passage and a bypass valve in the intake system of the diesel engine 10, that is, without complicating the system configuration. Both surge avoidance and re-acceleration performance can be achieved.

  By the way, in Embodiment 1 mentioned above, although the system which performs supercharging control so that an actual turbo rotational speed corresponds with a target turbo rotational speed was demonstrated, this invention is not limited to this, For example, The present invention can also be applied to a system that performs supercharging control so that the actual supercharging pressure matches the target supercharging pressure. Therefore, more specifically, for example, the feedback control of the supercharging pressure is performed so that the actual supercharging pressure of the turbocharger 30 matches the target supercharging pressure corresponding to the current operating state. In a diesel engine, when a surge is determined, the target boost pressure is fixed to the actual boost pressure immediately before the surge determination, and the VN opening is opened to avoid surge while The assist amount by the electric motor 32 may be increased so that the actual supercharging pressure is maintained.

  In the first embodiment described above, the electric motor 32 is provided as a mechanism for assisting the rotation of the compressor (centrifugal compressor) 30a. However, in the present invention, an assist mechanism for assisting the rotation of the centrifugal compressor. However, the present invention is not limited to this, and may be, for example, an air assist type assist mechanism that bleeds exhaust gas stored in a separate tank to the turbine of the turbocharger.

  In the first embodiment described above, the ECU 50 executes the process of step 110 or 118, so that the “surge determination means” in the first invention executes the process of step 114. The “supercharging state control means” in the first invention is realized. Further, in the first embodiment described above, the opening of the variable nozzle (VN) 30c is controlled to the open side to avoid a surge, whereby “the compressor speed is controlled” in the first aspect of the invention. As a result, the function of the supercharging state control means of causing a reduction in the exhaust pressure of the internal combustion engine is realized.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS.
The system of the present embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 6 described later instead of the routine shown in FIG. 4 using the hardware configuration shown in FIG.

[Features of Embodiment 2]
In the first embodiment described above, the control when a surge is detected during the operation of the electric motor 32 has been described. On the other hand, in this embodiment, control when a surge is detected when the electric motor 32 is not operated will be described. In the present embodiment, when a surge is detected when the motor 32 is not operating, the fuel injection amount Q is fixed to a value immediately before the surge determination, and the VN opening at the time of the surge determination is determined according to the operating region of the compressor 30a. The control speed is variable. Even when a surge is detected during the operation of the electric motor 32, the control of the present embodiment can be similarly applied.

  FIG. 6 is a flowchart of a routine executed by the ECU 50 in the second embodiment to realize the above function. In FIG. 6, the same steps as those shown in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 6, if it is determined that the surge determination flag is ON (step 110), then the fuel injection amount Q is fixed to a value immediately before the surge determination (step 200). More specifically, the ECU 50 stores the fuel injection amount Q for each predetermined sampling time. In this step 200, the fuel injection amount at a time several milliseconds before the time when the surge determination flag is turned on. Fixed to Q.

  Next, the control speed of the VN opening that is opened to avoid the surge is determined within the sensitivity range of the VN opening that is determined according to the operating region of the compressor 30a, and the determined control speed is obtained. The VN 30c is controlled (step 202). FIG. 7 is a diagram for explaining a method for determining the control speed of the VN opening degree in this step 202. FIG. 7A shows the relationship between the sensitivity of the VN opening degree and the pressure ratio P3 / P0 of the compressor 30a, and FIG. 7B shows the control speed of the VN opening degree and the pressure ratio P3 / P0 of the compressor 30a. The relationship with P0 is shown.

  The sensitivity when the VN 30c is opened by a predetermined amount, in other words, the degree of influence on the exhaust pressure due to the opening and closing of the VN 30c varies depending on the operating region of the compressor 30a. More specifically, the sensitivity of the VN opening degree tends to increase as the pressure ratio P3 / P0 increases. For this reason, as shown in FIG. 7B, the control speed of the VN opening is set so as to decrease as the pressure ratio P3 / P0 increases. In FIG. 7, the horizontal axis represents the pressure ratio P3 / P0, but the present invention is not limited to this, and the fuel injection amount Q may be substituted.

  In this step 202, the VN 30c is controlled to avoid a surge at the control speed of the VN opening degree according to the relationship shown in FIG. 7B. Next, assist by the electric motor 32 is executed so that the actual turbo speed immediately before the surge determination is maintained (step 204).

  Further, in the routine shown in FIG. 6, it is determined that the surge determination flag is OFF (step 118), and the amount of change in the engine speed NE and the amount of change in the intake air amount Ga are determined from their predetermined determination values. If it is determined that it has increased (step 124), then the VN opening is gradually feedback controlled so that the current actual turbo speed becomes the target turbo speed (step 206). Next, in conjunction with the feedback control of the VN opening, the assist amount of the electric motor 32 is gradually reduced (step 208).

  Next, the upper and lower limit guard values of the fuel injection amount Q fixed in step 200 are gradually returned to normal control in order to suppress the occurrence of combustion fluctuations (step 210).

  According to the routine shown in FIG. 6 described above, when a surge is determined, the fuel injection amount Q is fixed to a value immediately before the surge determination, and the VN opening is controlled to the open side to avoid surge. Thus, the turbo rotational speed that is reduced by this is maintained at a value equivalent to the actual turbo rotational speed immediately before the surge determination by the assist of the electric motor 32. For this reason, a surge can be avoided while suitably suppressing torque fluctuations in the diesel engine 10. Further, according to the processing of the above routine, the control speed of the VN opening is made variable within the sensitivity range of the VN opening corresponding to the operating region of the compressor 30a. For this reason, it is possible to avoid a surge while satisfactorily suppressing rapid fluctuations in the operating state of the diesel engine 10 and torque fluctuations resulting therefrom.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIG. 8 and FIG.
The system of the present embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 8 to be described later instead of the routine shown in FIG. 4 using the hardware configuration shown in FIG.

[Features of Embodiment 3]
The system of the present embodiment is characterized in that the control speed of the VN opening is made variable according to the magnitude of the generated surge. Even when a surge is detected during the operation of the electric motor 32, the control of the present embodiment can be similarly applied.

  FIG. 8 is a flowchart of a routine executed by the ECU 50 in the third embodiment to realize the above function. In FIG. 8, the same steps as those shown in FIG. 4 or 6 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 8, after the fuel injection amount Q is fixed to a value immediately before the surge determination (step 200), the magnitude of the surge that has occurred this time is then calculated (step 300). More specifically, the greater the above-described second-order differential value of the passing air amount Ga of the compressor 30a, the larger the surge magnitude is calculated.

  Next, the VN 30c is opened by the VN opening based on the calculated surge magnitude (step 302). FIG. 9 is an example of a map provided for the ECU 50 to determine the control speed of the VN opening based on the magnitude of the surge. As the surge increases, the surge cannot be avoided unless the VN opening is greatly opened. For this reason, the map shown in FIG. 9 is set so that the control speed of the VN opening degree increases as a large surge occurs. Instead of calculating the magnitude of the surge by the second-order differential value, the magnitude of the generated surge may be predicted by the following method, and the control speed of the VN opening may be made variable. That is, for example, the operating range of the compressor 30a determined by the relationship between the pressure ratio P3 / P0 of the compressor 30a and the intake air flow rate Ga, or the torque (or fuel injection amount Q) of the diesel engine 10 and the engine speed NE. The magnitude of the generated surge may be determined in advance in accordance with the operation range of the diesel engine 10 determined in relation to the above, and the control speed of the VN opening may be variable for each of these operation regions or operation regions.

  Next, assist by the electric motor 32 is executed so that the actual turbo speed immediately before the surge determination is maintained (step 304). Next, it is determined whether or not the surge determination flag is OFF (step 306). As a result, if the surge has not yet been avoided, the series of steps 300 to 304 is executed again. On the other hand, if it is determined in step 306 that the surge determination flag is OFF, A series of processes of the above-described step 124 and steps 206 to 210 are executed.

  According to the routine shown in FIG. 8 described above, an appropriate control speed of the VN opening degree can be determined according to the detected surge magnitude. For this reason, regardless of the magnitude of the detected surge, it is possible to quickly control the VN opening required to avoid the surge, and to improve the torque fluctuation of the diesel engine 10 due to the occurrence of the surge. Can be suppressed.

  In the third embodiment described above, the “surge level discriminating means” according to the fifth aspect of the present invention is realized by the ECU 50 executing the processing of step 300.

Others.
By the way, in Embodiments 1 to 3 described above, when it is determined that there is a surge, the actual turbo rotation speed (or actual supercharging pressure) immediately before the surge determination is maintained while controlling VN to the open side. Thus, the electric motor 32 assists the rotation of the compressor 30a. However, in the present invention, in order to avoid a surge during acceleration while ensuring good reacceleration performance after avoiding a surge, the following method may be used.

  FIG. 10 is a schematic configuration diagram for explaining the configuration of another embodiment of the present invention. In FIG. 19, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  The system shown in FIG. 10 further includes an intake bypass pipe 72 for bypassing the compressor 30a and a bypass valve 74 disposed in the middle of the intake bypass pipe 72 in the intake pipe 18 of the diesel engine 70. Except for the above, it has the same configuration as the system shown in FIG. More specifically, one end of the intake bypass pipe 72 is connected in the middle of the intake pipe 18 from the compressor 30a to the intercooler 26, and the other end is connected to the upstream side of the compressor 30a. The opening degree of the bypass valve 74 is controlled by the ECU 76.

  According to such a configuration including the bypass valve 74, by operating the bypass valve 74 to open the inlet of the intake bypass pipe 72, a part of the air compressed by the compressor 30a is returned again to the inlet side of the compressor 30a. It is. When the turbocharger 30 is in an operating state where a surge is likely to occur, a part of the air exiting the compressor 30a is returned to the inlet side of the compressor 30a through the intake bypass pipe 72, whereby the pressure ratio P3 before and after the compressor 30a is restored. Since / P0 decreases and the compressor passing air amount Ga increases, surge can be prevented.

  Therefore, in the present invention, in order to avoid a surge during acceleration while ensuring good reacceleration performance after avoiding a surge, the following control is performed using the configuration shown in FIG. May be. That is, the supercharging state control means of the present invention is not limited to the VN 30c but may be the bypass valve 74. Specifically, when it is determined that a surge has occurred, the bypass valve 74 is opened by a predetermined amount so that the compressor 30a is operated in the region near the surge line, while avoiding the surge and The assist amount by the electric motor 32 may be increased so that the actual supercharging pressure immediately before the determination is maintained (the assist is started when the electric motor 32 is not operated). According to such a method, the intake to the diesel engine 10 that is reduced by the control of the bypass valve 74 is reduced by opening the bypass valve 74 by a predetermined amount, thereby avoiding a surge by increasing the amount of air passing through the compressor 30a. The air amount Ga can be maintained at the level before the surge determination with the assistance of the electric motor 32.

  In another embodiment in which the bypass valve 74 is controlled, the opening degree of the bypass valve 74 is opened by a predetermined amount in order to avoid a surge, whereby the “supercharging pressure is controlled” in the first invention. As a result, the function of the supercharging state control means of causing a reduction in the amount of intake air to the internal combustion engine is realized.

  There is also known a diesel engine that includes an exhaust bypass passage (not shown) that bypasses the turbine 30b and an electrically-operated wastegate valve (not shown) disposed in the middle of the exhaust bypass passage. In a system including such a diesel engine, the supercharging state control means of the present invention may be one that adjusts the opening of the wastegate valve instead of adjusting the opening of the VN 30c. Specifically, when a surge is determined, the actual turbo speed (or actual boost pressure) immediately before the surge determination is maintained while avoiding the surge by opening the wastegate valve by a predetermined amount. As described above, the assist amount by the electric motor 32 may be increased (when the electric motor 32 is not operated, the assist is started).

  In another embodiment in which the waste gate valve is controlled, the opening of the waste gate valve is opened by a predetermined amount to avoid a surge, whereby the “supercharging pressure or compressor As a result of the control, the supercharging state control means function of “lowering the exhaust pressure of the internal combustion engine” is realized.

  In the above-described first to third embodiments or other examples, the case where the present invention is applied to the control device of the diesel engine 10 has been described. However, the present invention is a spark ignition internal combustion engine such as a gasoline engine. The present invention can also be applied to the control device.

It is a schematic block diagram for demonstrating the structure of Embodiment 1 of this invention. It is a figure which shows the relationship between the pressure ratio P3 / P0 before and behind a compressor, and the air flow amount Ga of a compressor. It is a figure for demonstrating the surge determination method of Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows the map which defined the base VN opening degree referred in the routine shown in FIG. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a figure for demonstrating the method of determining the control speed of VN opening degree in step 202 in FIG. It is a flowchart of the routine performed in Embodiment 3 of the present invention. It is an example of the map provided in order to determine the control speed of VN opening based on the magnitude | size of a surge. It is a schematic block diagram for demonstrating the structure of the other Example of this invention.

Explanation of symbols

10, 70 Diesel engine 12 Fuel injection valve 16 Intake manifold 18 Intake pipe 28 Supercharging pressure sensor 30a Compressor (centrifugal compressor)
30b Turbine 30 Turbocharger 30c Variable nozzle (VN)
32 Electric motor 34 Turbo speed sensor 50, 76 ECU (Electronic Control Unit)
52 Motor controller 72 Intake bypass pipe 74 Bypass valve

Claims (5)

A control device for an internal combustion engine including a centrifugal compressor in an intake passage,
Surge determining means for determining whether or not a surge has occurred in the centrifugal compressor;
When the surge determination means determines that a surge has occurred, the boost pressure or compressor speed is controlled to avoid the surge, and the boost pressure or compressor speed is controlled. As a result, a supercharging state control means for causing a reduction in exhaust pressure of the internal combustion engine or a reduction in the amount of intake air to the internal combustion engine,
When the supercharging pressure or the compressor speed is controlled by the supercharging state control means, assists the rotation of the centrifugal compressor so that the supercharging pressure or the compressor speed before the surge determination is maintained. An assist mechanism to
An internal combustion engine control device comprising a centrifugal compressor. The centrifugal compressor is configured as a compressor of a turbocharger with an electric motor,
The control device for an internal combustion engine having a centrifugal compressor according to claim 1, wherein the assist mechanism is the electric motor.   The control amount of the supercharging pressure or the compressor speed by the supercharging state control means is a minimum amount for maintaining the supercharging pressure or the compressor speed before the surge determination. An internal combustion engine control device comprising the centrifugal compressor according to claim 2.   The supercharging state control means makes the control speed of the supercharging pressure or the compressor rotational speed variable according to the operating region of the centrifugal compressor. The control apparatus of an internal combustion engine provided with the centrifugal compressor of description. Further comprising a surge level discriminating means for discriminating the magnitude of the surge;
The internal combustion engine having a centrifugal compressor according to any one of claims 1 to 4, wherein the control speed of the supercharging pressure or the compressor rotational speed is made variable in accordance with the magnitude of the determined surge. Engine control device.

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