JP2004225586A - Control device for multi-stage turbocharger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for a multi-stage turbocharger capable of operating a control system as a steady system, preventing surge of a compressor and operating a turbine in an efficient zone. <P>SOLUTION: This device is a control device for a multi-stage turbocharger in which a plurality of turbochargers are provided in series. The device is provided with an operation state detection means detecting an operation state of an engine, a control zone selection means selecting a control zone based on a detection result of the operation state detection means, and a feed back control means controlling with giving priority to keeping pressure ratio by at least one turbocharger constant in a predetermined control zone selected by the control zone selection means and performing feed back control based on target supercharging pressure and actual supercharging pressure by other turbochargers. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-stage turbocharger control device for an engine, particularly an automobile engine.
[0002]
[Prior art]
In recent years, there has been a tendency to increase the supercharging pressure to near the limit of the strength of the engine, that is, to increase the supercharging pressure due to a demand for both low fuel consumption and high output of the engine. To increase the supercharging pressure, a so-called multi-stage turbocharger in which a plurality of turbochargers are provided in series in an engine has been proposed. In such a multi-stage turbocharger, the final supercharging pressure is obtained by a plurality of compressors. However, if the control is not performed properly, a drive loss is caused or the system efficiency is reduced.
[0003]
Therefore, various control devices aiming at optimizing the control of such a multi-stage turbocharger have been proposed, and among them, for example, one described in Patent Document 1 is known.
[0004]
The one described in Patent Document 1 includes a high-, medium-, and low-pressure stage turbine and a high-, medium-, and low-pressure stage compressor driven by these turbines in an exhaust path, and further allows exhaust gas to bypass the turbine. Turbine-side bypass path that supplies air directly from the upstream side to the downstream side, a compressor-side bypass path that returns intake air from the downstream side to the upstream side by bypassing the compressor, and a wastegate that controls the exhaust flow rate of the turbine-side bypass path. A valve and a bleed valve for controlling the intake flow rate of the compressor-side bypass passage are provided. Then, in order to obtain a predetermined supercharging pressure, a waste gate valve and a bleed valve are used by using a signal from a pressure sensor provided on the downstream side of the compressor so that the pressure ratios of the compressors of the respective stages become equal. And to control.
[0005]
[Patent Document 1]
JP-A-11-315725
[Problems to be solved by the invention]
However, the one described in Patent Document 1 has been proposed for a reciprocating engine for an aircraft capable of flying for a long time in a high altitude area at an altitude of 25 km or more. There is not much merit in controlling the pressure ratios of the compressors to be equal. On the contrary, if control is performed so that the pressure ratios of the compressors of the respective stages become equal, in a vehicle engine having a large load variation due to the accelerator operation, the stability of the control is impaired due to the hysteresis of the control. This is because large fluctuations occur and adversely affect drivability.
[0007]
Accordingly, an object of the present invention is to solve such a conventional problem, to enable a control system to operate as a stable system, to prevent a compressor surge, and to enable a turbine to operate in a high efficiency region. To provide a control device.
[0008]
[Means for Solving the Problems]
A control device for a multi-stage turbocharger according to one embodiment of the present invention that solves the above problems is a control device for a multi-stage turbocharger in which a plurality of turbochargers are provided in series, and an operation state detection unit that detects an operation state of an engine. A control area selecting means for selecting a control area based on a detection result of the operating state detecting means; and a pressure ratio by at least one turbocharger being substantially constant in a predetermined control area selected by the control area selecting means. And feedback control means for performing feedback control by another turbocharger based on the target supercharging pressure and the actual supercharging pressure.
[0009]
According to such a configuration, the number of control targets can be reduced, and the system can be operated as a stable system.
[0010]
Here, it is preferable that the plurality of turbochargers are variable capacity turbochargers having a variable flow rate mechanism in a turbine nozzle portion.
[0011]
Further, it is preferable that the predetermined control region is a control region in which the number of revolutions of the engine is equal to or higher than a predetermined value and the request for increasing the engine output torque is equal to or higher than the predetermined value.
[0012]
Furthermore, it is preferable that the high-pressure stage turbocharger be controlled preferentially so that the pressure ratio becomes substantially constant.
[0013]
Further, in an area other than the predetermined control area, an open control that opens and controls the plurality of turbochargers based on a control value stored in a map so as to obtain a predetermined supercharging pressure corresponding to an operating state of the engine. It is preferable to have control means.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the accompanying drawings.
[0015]
FIG. 1 is a diagram showing an outline of a control device for a multi-stage turbocharger according to the present embodiment, in which the present invention is applied to a multi-stage turbocharger in which two variable capacity turbochargers having variable nozzles are arranged in series. It is.
[0016]
As shown in the drawing, a high-pressure stage turbine 14 and a low-pressure stage turbine 16 are provided in series in the exhaust path 12 of the engine 10 at intervals in the flow direction of the exhaust gas. The high pressure stage compressor 20 and the low pressure stage compressor 22 are interposed in series at intervals in the flow direction of the intake air. The high-pressure compressor 20 and the high-pressure turbine 14 are connected by a rotating shaft 24 to form a high-pressure turbocharger 26. The low-pressure compressor 22 and the low-pressure turbine 16 are connected by a rotating shaft 28 to form a low-pressure turbocharger 30. Is composed.
[0017]
A first intercooler 32 is provided in an intake path 18 between the low-pressure compressor 22 and the high-pressure compressor 20, and a second intercooler 32 is provided in the intake path 18 between the high-pressure compressor 20 and the engine 10. An intercooler 34 is provided. These are for cooling the intake air whose temperature has been raised by compression, but are not necessarily required for the constitution of the present invention, and either one or neither of them may be present.
[0018]
The exhaust passage 12 is provided with a bypass passage 36 connected to the upstream side of the high-pressure turbine 14 and the downstream side of the low-pressure turbine 16 so as to bypass the high-pressure turbine 14 and the low-pressure turbine 16. An exhaust bypass valve 38 is provided in the bypass passage 36. The opening degree of the exhaust bypass valve 38 is adjusted by an actuator (not shown) to adjust the flow rate of the exhaust gas flowing in the bypass passage 36. The operation of the actuator is controlled by the control unit 40 as described later.
[0019]
A first pressure sensor 42 for detecting the atmospheric pressure P1 is provided in the intake path 18 on the upstream side of the low-pressure stage compressor 22, and a high-pressure stage compressor is provided in the intake path 18 between the high-pressure stage compressor 20 and the first intercooler 32. A second pressure sensor 44 for detecting an inlet pressure P2 of the compressor 20; and a third pressure sensor for detecting an outlet pressure P3 of the high-pressure compressor 20 in the intake passage 18 between the high-pressure compressor 20 and the second intercooler 34. 46 are provided.
[0020]
Further, the engine 10 is provided with a rotation speed sensor 48 for detecting the rotation speed Ne of the engine 10 and an accelerator opening sensor 50 for detecting a load (accelerator opening A). The first pressure sensor 42, the second pressure sensor 44, the third pressure sensor 46, the rotation speed sensor 48, and the accelerator opening sensor 50 are connected to the control unit 40, and the output of each sensor is sent to the control unit 40. It is supposed to be.
[0021]
Further, the high-pressure stage turbine 14 of the high-pressure stage turbocharger 26 and the low-pressure stage turbine 16 of the low-pressure stage turbocharger 30 have variable nozzles VNH and VNL as variable flow mechanisms at their turbine nozzles. The control unit 40 constituted by a microcomputer or the like controls the variable nozzles VNH and VNL in accordance with the output values sent from the respective sensors as described later in order to obtain a predetermined supercharging pressure.
[0022]
Here, the opening degree setting map M used for selecting the control area and controlling the variable nozzles VNH and VNL will be described with reference to FIG. The opening setting map M is obtained by taking the accelerator opening A representing the load of the engine on the ordinate and the engine speed Ne on the abscissa, and in the open control region of the operation region of the engine 10 other than the feedback control region. , The variable nozzles VNH and VNL represent the opening to be taken, and the control value thereof is an optimum value experimentally obtained in accordance with, for example, the required characteristics of the engine. The opening degree setting map M is stored in a table of the control unit 40.
[0023]
Here, in the present embodiment, in the left side of the opening degree setting map M, in other words, in the region R1 which is a substantially low speed region of the engine 10, the variable nozzles VNH and VNL are both set to be fully closed. ing. Further, in a region R2 which is a region from a middle speed to a high speed under substantially the middle load of the engine 10, the variable nozzles VNH and VNL are set so as to gradually increase the opening degree from the middle opening to the full opening from the upper left to the lower right. . It should be noted that the step exists on the boundary between the region R1 and the region R2 because the variable nozzles VNH and VNL are fully closed in the region from the light load region of the engine 10 to the middle speed region (the right region of the region R1). By doing so, the back pressure is increased, and the exhaust gas recirculation (EGR) to the intake system is improved.
[0024]
Here, “fully closed” of the variable nozzle means a state in which the nozzle is narrowed to the minimum flow path area, “full open” of the variable nozzle means a state in which the nozzle is opened to the maximum flow area, and “ The “medium opening” means a state in which, for example, a movable vane driven by an actuator (not shown) is positioned such that the nozzle has a flow area between the minimum flow area and the maximum flow area. I do.
[0025]
Further, in a high load region where the request for increasing the output torque of the engine 10 is equal to or higher than a predetermined value, and in a region where the speed is higher than a medium speed, the specific opening of the variable nozzles VNH and VNL is not set, and the opening of the variable nozzles VNH and VNL is not set. The degree is appropriately changed, and a region RFB is set in which the feedback control of the supercharging pressure P3 is performed. As a result, open control of the supercharging pressure P3 is performed in the regions R1 and R2, whereas feedback control is performed in the region RFB. The open control areas R1 and R2 and the feedback control area RFB are not fixed, and their boundaries are appropriately set according to the required characteristics of each engine.
[0026]
Next, an example of a control routine by the control unit 40 in the embodiment of the present invention will be described with reference to the flowchart of FIG. When the engine is started and the control is started, in the control routine of the multi-stage turbocharger by the control unit 40, in step S1, the operation of the operating state detecting means for detecting the operating state of the engine is performed by the rotational speed sensor 48 to detect the current engine speed. While the number Ne is detected, the current accelerator opening A is detected by the accelerator opening sensor 50, and the detected current engine speed Ne and the current accelerator opening A are read into the control unit 40.
[0027]
Next, in step S2, the current engine speed Ne and the accelerator opening A detected in step S1 are stored and stored in a table in the control unit 40 with reference to the opening setting map M shown in FIG. Is done. Then, the process proceeds to step S3, where it is determined whether or not the operation state is the boost pressure feedback control region RFB as an operation of the control region selection means. If NO, that is, if the open control region R1 or R2, the operation proceeds to step S4. The control is performed such that the opening degrees of the variable nozzles VNH and VNL become equal to the opening degrees set in the opening degree setting map M corresponding to the operating state. By controlling the opening of the variable nozzles VNH and VNL while referring to the predetermined opening set in the opening setting map M, the high-pressure turbine 14 and the low-pressure stage 14 are adjusted in accordance with the operating state of the engine 10. The exhaust gas flow characteristic of the turbine 16 is controlled, and a desired supercharging pressure optimal for the operating state of the engine 10 can be obtained by the high-pressure compressor 20 and the low-pressure compressor 22.
[0028]
On the other hand, if the determination in step S3 as to whether or not the operating state is in the supercharging pressure feedback control region RFB is YES, the process proceeds to step S5, and thereafter, control is performed as the operation of the feedback control means. That is, in step S5, first, the first, second, and third pressure sensors 42, 44, and 46 detect the atmospheric pressure P1, the pressure P2 downstream of the low-pressure stage compressor 22, that is, the pressure P2 upstream of the high-pressure stage compressor 20, and the like. The pressure on the downstream side, that is, the supercharging pressure P3 is detected, and each value thereof is read into the control unit 40. Next, in step S6, the control unit 40 calculates a target supercharging pressure f (Ne, A) based on the current engine speed Ne and the accelerator opening A already read in step S1. Then, the process proceeds to step S7, and it is determined whether the current actual supercharging pressure P3 is larger than the target supercharging pressure f (Ne, A).
[0029]
If the current actual supercharging pressure P3 is larger than the target supercharging pressure f (Ne, A), the process proceeds to step S8, and it is determined whether or not the variable nozzles VNH and VNL are fully opened. Note that the current opening of the variable nozzles VNH and VNL can be determined by using a detection signal from an opening sensor (not shown) provided in the variable nozzles VNH and VNL, or by using the setting opening used in the previous control routine. The determination can be made using the degree value data. Here, when the variable nozzles VNH and VNL are already fully opened, the process proceeds to step S9, the exhaust bypass valve 38 is adjusted by a predetermined amount in the opening direction, and the flow rate of the exhaust gas to the high-pressure turbine 14 and the low-pressure turbine 16 is adjusted. Is controlled to reduce the supercharging pressure P3.
[0030]
If the current supercharging pressure P3 is larger than the target supercharging pressure f (Ne, A), but it is determined in step S8 that the variable nozzles VNH and VNL are not fully opened, the process proceeds to step S10, and the high-pressure turbo A pressure ratio P3 / P2 of the high-pressure stage compressor 20 of the charger 26 and a target pressure ratio g (Ne, A) in the current operating state based on the current engine speed Ne and the accelerator opening A are calculated.
[0031]
Next, in step S11, the calculated current pressure ratio P3 / P2 by the high-pressure compressor 20 is compared with the target pressure ratio g (Ne, A). When the pressure ratio P3 / P2 of the high-pressure stage is greater than the target pressure ratio g (Ne, A), the control unit 40 proceeds to step S12, and increases the opening of the variable nozzle VNH of the high-pressure stage turbocharger 26 in the direction of increasing the opening degree. If the pressure ratio of the high-pressure stage P3 / P2 ≦ the target pressure ratio g (Ne, A), the process proceeds to step S13, in which the opening degree of the variable nozzle VNL of the low-pressure stage turbocharger 30 is controlled to increase. .
[0032]
On the other hand, if it is determined in step S7 that the current supercharging pressure P3 is equal to or less than the target supercharging pressure f (Ne, A), the process proceeds to step S14, and similarly to step S10, the high-pressure stage turbocharger 26 And the target pressure ratio g (Ne, A) based on the current engine speed Ne and the accelerator opening A are calculated in step S15. The pressure ratio P3 / P2 is compared with the target pressure ratio g (Ne, A). When the pressure ratio P3 / P2 of the high-pressure stage is greater than the target pressure ratio g (Ne, A), the control unit 40 proceeds to step S16, and in the direction in which the opening of the variable nozzle VNL of the low-pressure stage turbocharger 30 is reduced. If the pressure ratio of the high-pressure stage P3 / P2 ≦ the target pressure ratio g (Ne, A), the process proceeds to step S17, in which the opening degree of the variable nozzle VNH of the high-pressure stage turbocharger 26 is reduced.
[0033]
The control routine by the control unit 40 is executed at a predetermined time period, and by repeatedly executing the routine, the supercharging pressure P3 is feedback-controlled to the target supercharging pressure in the supercharging pressure feedback control region RFB. Will be done. At this time, in the above-described embodiment, first, the pressure ratio P3 / P2 of the high-pressure stage is controlled so as to approach the target pressure ratio g (Ne, A), and the pressure ratio by the high-pressure stage turbocharger 26 is substantially constant. It is controlled with priority so that By doing so, the applicable engine speed range can be widened, the balance between the compressor and the turbine of each of the high-pressure stage turbocharger 26 and the low-pressure stage turbocharger 30 is good, and turbo efficiency can be easily obtained.
[0034]
Here, the control of the multi-stage turbocharger of the engine 10 including the above-described supercharging pressure feedback will be described more specifically. For example, assuming that the engine 10 is accelerated from a low-speed, low-load operation state to a full-load (or high-load) operation state when the accelerator pedal is rapidly depressed, such as when the vehicle starts, As is well known, the rotational speed does not immediately rise, and the operating state first shifts to above the region R1. However, the variable nozzles VNH and VNL are kept fully closed by the setting in the opening degree setting map M. If the accelerator opening A is maintained in this state, the operating state shifts to the supercharging pressure feedback control region RFB near the engine speed Ne0 as the engine speed increases. Here, the relationship between the opening degrees of the variable nozzles VNH and VNL and the engine speed Ne in the supercharging pressure feedback control region RFB is as shown in FIG. 4, and the high-pressure stage variable nozzle VNH Priority control is performed so that the pressure ratio P3 / P2 of the high pressure stage becomes substantially constant, and the supercharging pressure of the variable nozzle VNL of the low pressure stage is feedback-controlled, so that the opening degree of the variable nozzle VNH of the high pressure stage is also reduced. The opening of the low-pressure stage variable nozzle VNL is also controlled so as to increase continuously as the engine speed Ne increases. Here, the engine speed Ne0 represents the engine speed near the boundary between the region R1 and the feedback control region RFB in FIG.
[0035]
Therefore, the shift from the open control region R1 to the feedback control region RFB is performed in a state in which the variable nozzles VNH and VNL are fully closed, so that a large change in the supercharging pressure does not occur, and the subsequent increase in the rotational speed. Accordingly, the variable nozzles VNH and VNL are continuously changed in the opening direction, so that stable control is possible. That is, if the opening and closing of the variable nozzles VNH and VNL are repeated, the stability of the control is impaired due to the hysteresis. However, such a case is caused when the variable nozzles VNH and VNL are continuously changed in the opening direction. There is no control. Further, assuming a case where the accelerator pedal is suddenly depressed from the medium speed and the medium load operation state to the full load or high load operation state, the operation state of the engine 10 is controlled by the feedback control from the region R2. The process moves to the region RFB. In this case, assuming that the engine speed Ne1 shifts from the region R2 to the feedback control region RFB, the variable nozzles VNH and VNL are opened near the boundary between the region R2 and the feedback control region RFB at the engine speed Ne1 in the region R2. Since the degree is set in the opening degree setting map M so that the change at the time of the transition is suppressed, a large change in the supercharging pressure occurs as in the case of the transition from the area R1 to the feedback control area RFB. In addition, as the number of rotations increases thereafter, the variable nozzles VNH and VNL are continuously changed in the opening direction, and stable control is possible.
[0036]
In the above, the embodiment has been described in which the pressure ratio P3 / P2 of the high-pressure stage is prioritized and control is performed so as to approach the target pressure ratio g (Ne, A). However, although a certain reduction in turbo efficiency cannot be denied, it goes without saying that control can be performed so as to approach the target pressure ratio g (Ne, A) by giving priority to the pressure ratio P2 / P1 of the low pressure stage. Absent.
[0037]
Further, in the above-described embodiment, an example in which the present invention is applied to a variable displacement turbocharger having a variable nozzle has been described. However, the present invention is also applicable to a multistage turbocharger having a waste gate valve. The same applies by controlling the opening of the wastegate valve instead of controlling the opening.
[0038]
In the above-described embodiment, the target pressure ratio g (Ne, A) of the pressure ratio P3 / P2 of the high pressure stage in the feedback control region RFB increases and decreases as the engine speed increases, as shown in FIG. , But may always take a constant value regardless of the engine speed.
[0039]
Furthermore, in the above-described embodiment, the high-pressure stage outlet pressure P3 detected by the pressure sensor 46 provided at the outlet of the high-pressure stage compressor 20 is used as the supercharging pressure. Alternatively, the intake pipe pressure Pb detected by the intake pipe pressure sensor may be used instead.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an outline of a multi-stage turbocharger control device according to an embodiment of the present invention.
FIG. 2 is an opening setting map used for selecting a control area and controlling variable nozzles VNH and VNL in the control according to the embodiment of the present invention.
FIG. 3 is a flowchart illustrating an example of a control procedure of the multi-stage turbocharger control device according to the embodiment of the present invention.
FIG. 4 is a graph showing the opening degrees of variable nozzles VNH and VNL of the multi-stage turbocharger according to one embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 10 engine 14 high-pressure turbine 16 low-pressure turbine 20 high-pressure compressor 22 low-pressure compressor 26 high-pressure turbocharger 30 low-pressure turbocharger 36 bypass passage 38 exhaust bypass valve 40 control unit 42 first pressure sensor 44 second pressure sensor 46 3 pressure sensor 48 rotation speed sensor 50 accelerator opening sensor VNH high-pressure turbine variable nozzle VNL low-pressure turbine variable nozzle

Claims (5)

A multi-stage turbocharger control device provided with a plurality of turbochargers in series,
Operating state detecting means for detecting an operating state of the engine;
Control region selecting means for selecting a control region based on the detection result of the operating state detecting means,
In the predetermined control region selected by the control region selection means, control is performed preferentially so that the pressure ratio of at least one turbocharger is substantially constant, and the target supercharging pressure and the actual supercharging are controlled by another turbocharger. Feedback control means for performing feedback control based on the pressure and
A control device for a multi-stage turbocharger, comprising: The control device for a multi-stage turbocharger according to claim 1, wherein the plurality of turbochargers are variable capacity turbochargers having a variable flow rate mechanism in a turbine nozzle unit. 3. The control device for a multi-stage turbocharger according to claim 1, wherein the predetermined control region is a control region in which the engine speed is equal to or higher than a predetermined value and an engine output torque increase request is equal to or higher than a predetermined value. . 4. The control device for a multi-stage turbocharger according to claim 1, wherein the high-pressure stage turbocharger is preferentially controlled so that the pressure ratio becomes substantially constant. In an area other than the predetermined control area, an open control unit that performs open control of the plurality of turbochargers based on a control value stored and set in a map to obtain a predetermined supercharging pressure according to an operating state of the engine. The control device for a multi-stage turbocharger according to any one of claims 1 to 4, further comprising:

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