JP2009180162A - Turbocharger control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a turbocharger control system for an internal combustion engine wherein boost pressure is controlled by controlling nozzle-opening on the inlet side of an exhaust turbine, and over-revolution of the turbine is prevented. <P>SOLUTION: The number of revolutions of the turbine is directly or indirectly detected, and the periods of time when the number of turbine revolutions exceeds a critical number of revolutions are accumulated. When the accumulated time T exceeds a first threshold T1, only in transient operation, a minimum value of the nozzle-opening is controlled to the open side (S31, S32). When the accumulated time T exceeds further a second threshold T2, both in stationary and in transient operations, a minimum valve of the nozzle-opening is controlled to the open side (S33, S34). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a turbocharger control device for an internal combustion engine that controls a supercharging pressure by controlling a nozzle opening (nozzle area) on the inlet side of an exhaust turbine, and more particularly to a technique for preventing the overspeed.

Patent Document 1 shows a variable capacity turbocharger capable of controlling the supercharging pressure by changing the nozzle flow rate and the exhaust pressure by changing the nozzle opening (nozzle area) on the inlet side of the exhaust turbine. Yes. When the boost pressure (boost pressure) is equal to or higher than the set value, and when the turbine speed is equal to or higher than the set value even if the boost pressure is less than the set value, the nozzle opening (nozzle area) is set. The exhaust turbine is prevented from over-rotation by forcibly controlling the operation to the maximum value.
JP-A-5-280365

  However, in order to prevent over-rotation of the exhaust turbine, if the nozzle opening is controlled to the maximum value when the turbine speed is greater than or equal to the set value, the turbine speed may increase temporarily and momentarily. Even if it does not lead to high cycle fatigue, the supercharging will be stopped immediately. Therefore, drivability is deteriorated by frequently stopping supercharging.

  In view of such a situation, an object of the present invention is to more appropriately prevent over-rotation of an exhaust turbine.

  For this reason, in the present invention, the time during which the turbine rotational speed exceeds the predetermined limit rotational speed is accumulated, and the minimum value of the nozzle opening is opened when the cumulative over-rotation time exceeds the threshold value. The configuration is limited to the side.

  According to the present invention, by controlling based on the accumulated over-rotation time, it is possible to prevent over-rotation that leads to high cycle fatigue without being affected by an instantaneous increase in the turbine speed.

  In order to prevent over-rotation, limiting the minimum value of the nozzle opening to the open side prevents over-rotation without stopping super-charging and minimizing the impact on super-charging pressure control. Can be prevented.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an internal combustion engine with a turbocharger (here, a diesel engine) showing an embodiment of the present invention.

  In the diesel engine 1, the intake passage 3 from the air cleaner 2 is provided with an intake compressor 5 of a variable capacity turbocharger 4. Accordingly, the intake air is supercharged by the intake compressor 5, cooled by the intercooler 6, and flows into the combustion chamber of each cylinder through the collector 7. The fuel is directly injected into the combustion chamber from the fuel injection valve 8 of each cylinder. The air that has flowed into the combustion chamber and the injected fuel are combusted by compression ignition, and the exhaust gas flows out to the exhaust passage 9.

The exhaust gas flowing into the exhaust passage 9 passes through the exhaust turbine 10 of the variable capacity turbocharger 3 and drives it.
The variable capacity turbocharger 3 includes an exhaust turbine 10 driven by exhaust gas, an intake compressor 5 that is driven by the exhaust turbine 10 to supercharge intake air, and guides exhaust gas to an inlet of the exhaust turbine 10. The movable nozzle vane 11 is provided so that the nozzle opening degree (nozzle area) can be controlled, and the negative pressure actuator 12 that drives the movable nozzle vane 11 via a link mechanism.

  Therefore, the nozzle opening degree (nozzle area) can be controlled by the negative pressure actuator 12 for driving the movable nozzle vane 11, and the exhaust gas acting on the exhaust turbine 10 can be controlled by controlling the nozzle opening degree (nozzle area) to the large side. The flow rate and the exhaust pressure can be reduced, the turbine rotational speed can be reduced, and the supercharging pressure can be reduced. Conversely, by controlling the nozzle opening (nozzle area) to the small side, the exhaust flow rate and the exhaust pressure acting on the exhaust turbine 10 can be increased, the turbine rotation speed can be increased, and the supercharging pressure can be increased. it can.

  The controlled negative pressure to the negative pressure actuator 12 is the negative pressure from the reservoir tank 15 which is a negative pressure source in the atmosphere from the atmosphere introduction port 14 provided on the clean side of the air cleaner 2 by the duty controlled linear solenoid valve 13. Make by diluting the pressure. The reservoir tank 15 is connected to a negative pressure pump 18 driven by the engine 1 through a one-way valve 16 and an orifice 17.

The duty control of the linear solenoid valve 13 is performed by an engine control unit (ECU) 20.
In other words, the ECU 20 determines the duty (DUTY) for controlling the nozzle opening, and drives the linear solenoid valve 13 with this duty to control the control negative pressure to the negative pressure actuator 12, thereby making it movable. The nozzle vane 11 is driven to control the nozzle opening (nozzle area).

The relationship between the duty and the nozzle opening is as shown in FIG.
That is, on the small duty side (0% side), the nozzle opening degree can be increased, and at this time, the supercharging pressure can be controlled to decrease. On the contrary, on the large duty side (100% side), the nozzle opening can be made small, and at this time, the supercharging pressure can be controlled to the increase side. During normal operation, the maximum opening is obtained at a duty of 0%, and the minimum opening is obtained at a duty of 100%.

  The ECU 20 includes an accelerator opening sensor 21 that detects the accelerator opening APO, an engine speed sensor 22 that detects the engine speed Ne, an air flow meter 23 that detects the intake air amount Qa, for controlling the boost pressure, etc. Signals are input from an atmospheric pressure sensor 24 that detects atmospheric pressure, a boost pressure sensor 25 that detects boost pressure (boost pressure), a gear position sensor 26 that detects the gear position of the transmission, and the like.

  Further, the ECU 20 calculates and controls the fuel injection amount Qf of the fuel injection valve 8 from the accelerator opening APO and the engine speed Ne, and this fuel injection amount Qf is also used for controlling the supercharging pressure and the like.

FIG. 2 is a flowchart of a supercharging pressure control (nozzle opening degree control) routine executed by the ECU 20.
In S1, it is determined whether the operation state is a steady operation state or a transient operation state. Specifically, the rate of increase (change amount per predetermined time) of the engine speed Ne is compared with a predetermined value, and when it is less than the predetermined value, it is determined as a steady operation state, and when it is above the predetermined value, the transient operation state is determined. judge.

  In the case of the steady operation state, the process proceeds to S2, and the basic duty (basic DUTY) is set from the exhaust flow rate (intake air amount Qa + fuel injection amount Qf) with reference to the steady basic duty map for each gear position.

  In the case of the transient operation state, the process proceeds to S3, and the basic duty (basic DUTY) is set from the exhaust flow rate (intake air amount Qa + fuel injection amount Qf) with reference to the transient basic duty map for each gear position.

  In both the steady basic duty map and the transient basic duty map, the basic duty is set to be small so that the nozzle opening increases as the exhaust flow rate (exhaust energy at the turbine inlet) increases. Further, the basic duty may be set based on the exhaust gas flow rate and the EGR rate in consideration of the EGR rate if necessary. Further, the basic duty may be set from the engine speed and the load (fuel injection amount).

After S2 or S3, the process proceeds to S4.
In S4, the target boost pressure map is referred to, and the target boost pressure is set from the engine speed Ne and the fuel injection amount Qf.

In S5, the actual boost pressure (actual boost pressure) is detected by the boost pressure sensor 25, and the actual boost pressure and the target boost pressure are compared for feedback control.
If the actual boost pressure is smaller than the target boost pressure, the process proceeds to S6, and the correction duty (correction DUTY) is increased to increase the actual boost pressure (to decrease the nozzle opening).

When the actual supercharging pressure> the target supercharging pressure, the process proceeds to S7, and the correction duty (correction DUTY) is decreased in order to decrease the actual supercharging pressure (increase the nozzle opening degree).
After S6 or S7, the process proceeds to S8.

In S7, the final duty is calculated by adding the correction duty to the basic duty as in the following equation.
Final DUTY = Basic DUTY + Correction DUTY
Thereafter, during normal operation, the process proceeds to S13 after the determinations of S9 and S10.

  In S9, the value of the second flag F2 that is set when the later-described over-rotation accumulated time is equal to or greater than the second threshold value is determined. In S10, the later-described over-rotation accumulated time is the first. The value of the first flag F1 that is set when the threshold value is equal to or greater than 1 is determined. During normal operation, F1 = 0 and F2 = 0, so the determinations of S9 and S10 (both are NO) ), The process proceeds to S13.

  In S13, the final duty (final DUTY) is output to the linear solenoid valve 13. Thereby, the control negative pressure to the negative pressure actuator 12 is controlled, the variable nozzle vane 11 is driven, the nozzle opening degree is controlled, and the supercharging pressure is controlled. At this time, the final duty is controlled in the range of 0 to 100%, and the nozzle opening is controlled in the range of the maximum value to the minimum value correspondingly (see FIG. 5).

Processing (S11, S12, S14) when the first flag F1 = 1 or the second flag F2 = 1 will be described later.
FIG. 3 is a flowchart of the over-rotation accumulated time calculation routine, which is executed every predetermined time (ΔT).

In S21, the compressor inlet pressure Pin is estimated from the atmospheric pressure detected by the atmospheric pressure sensor 24 and the intake air amount Qa.
In S22, the compressor outlet pressure Pout is estimated from the boost pressure detected by the boost pressure sensor 25 and the intake air amount Qa.

In S23, the compressor pressure ratio PR = Pout / Pin is calculated from the compressor inlet pressure Pin and the compressor outlet pressure Pout.
In S24, a compressor pressure ratio (limit compressor pressure ratio) PRlimit when the turbine speed is a predetermined limit speed is calculated from the intake air amount Qa.

In S25, the actual compressor pressure ratio PR calculated in S23 is compared with the limit compressor pressure ratio PRlimit calculated in S24.
As a result of comparison, if PR> PRlimit, it is assumed that the engine is in an overspeed state (the turbine speed exceeds the limit speed), and ΔT, which is the execution time interval of this routine, is added to the previous overspeed accumulated time T. The over-rotation accumulated time T is updated by addition (T = T + ΔT).

In the case of PR <PRlimit, since the engine is not in an overspeed state, this routine is terminated as it is (without updating the overspeed accumulated time T).
FIG. 6 is a turbine rotational speed map in which the intake air amount Qa is on the horizontal axis and the compressor pressure ratio PR is on the vertical axis, and shows the limit rotational speed line particularly adapted to the transient operation state. .

  Therefore, using this map, the turbine rotational speed can be estimated from the intake air amount Qa and the compressor pressure ratio PR, and the estimated value of the turbine rotational speed is compared with a predetermined limit rotational speed. In the case of the limit rotational speed (when it is outside the limit rotational speed line on the map of FIG. 6), it can be determined that the engine is in an overspeed state.

  For this reason, in the present embodiment, a compressor pressure ratio (limit compressor pressure ratio) PRlimit corresponding to the limit rotational speed is made into a table corresponding to the intake air amount Qa, and the actual table is referred to in S24 by referring to this table. The limit compressor pressure ratio PRlimit is obtained from the intake air amount Qa. In S25, it is determined whether or not the actual compressor pressure ratio PR exceeds the limit compressor pressure ratio PRlimit, thereby determining whether or not the turbine speed exceeds the limit speed (overspeed state). Judgment.

  As for the table, as shown in the engine operating line in FIG. 6, since the engine behaves substantially along this line, the intake air amount Qave at the intersection of the limit rotational speed line and the engine operating line is calculated. A compressor pressure ratio (limit compressor pressure ratio) PRlimit corresponding to the limit rotational speed may be tabulated in a predetermined range (Qave −3σ to Qave + 3σ) as the center, corresponding to the intake air amount Qa. That is, it is sufficient to have only the data of the thick line portion in the limit rotational speed line in FIG. By using such a table, it is possible to reduce the ROM capacity and the matching man-hours.

  FIG. 4 is a flowchart of the over-rotation accumulated time determination routine, and the over-rotation accumulated time T calculated in the routine of FIG. 3 is determined. For the determination, the first to third threshold values T1 to T3 are used, and T1 <T2 <T3.

In S31, the over-rotation accumulated time T is compared with the first threshold value T1, and it is determined whether or not T> T1.
If the over-rotation accumulated time T exceeds the first threshold value T1, the process proceeds to S32, and the minimum value of the nozzle opening is limited to the open side only during steady operation between steady operation and transient operation. Thus, the first flag F1 is set (F1 = 1).

In S33, the over-rotation accumulated time T is compared with the second threshold value T2, and it is determined whether T> T2.
When the over-rotation accumulated time T exceeds the second threshold value T2, the process proceeds to S34, and the minimum value of the nozzle opening is limited to the open side in both the steady operation and the transient operation. 2 The flag F2 is set (F2 = 1).

In S35, the over-rotation accumulated time T is compared with the third threshold value T3, and it is determined whether or not T> T3.
When the over-rotation accumulated time T exceeds the third threshold value T3, the process proceeds to S36 and shifts to a safe mode in which at least the driver is warned of an abnormal state. In this safe mode, the driver is informed of an abnormal state by a warning message or the like to prompt inspection or repair, and if necessary, fail-safe processing such as engine output restriction may be executed.

Next, processing when the first flag F1 = 1 and further the second flag F2 = 1 in the routine of FIG. 4 will be described with reference to FIG.
When the over-rotation cumulative time T exceeds the first threshold value T1 and the first flag F1 = 1, the process proceeds to S11 in the determination in S10 of FIG.

In S11, it is determined whether or not the transient basic duty map is being used (the process proceeds to S3 in the determination in S1 and is in a transient operation state).
When not in the transient operation state (in the steady operation state), the process proceeds to S13 as usual, and the final duty (final DUTY) is output.

In the case of the transient operation state, the process proceeds to S12, where the final duty (final DUTY) is compared with a limit value X (for example, 90%) to determine whether or not the final DUTY> X.
When the final DUTY> X, the process proceeds to S14, and the limit value X is output instead of the final DUTY. That is, the minimum value of the nozzle opening is limited to the open side by limiting the maximum value of the duty to about 90%.

When the final DUTY <X, the process proceeds to S13 as usual, and the final duty (final DUTY) is output.
Thus, when the over-rotation cumulative time T exceeds the first threshold value T1, the minimum value of the nozzle opening is limited to the open side during transient operation. That is, as shown in FIG. 7, the minimum opening is limited by providing a DUTY limit value X and controlling the duty within a range from 0% to X.

When the over-rotation accumulated time T exceeds the second threshold value T2 and the second flag F1 = 1, the process proceeds to S12 in the determination in S9 of FIG.
In S12, the final duty (final DUTY) is compared with a limit value X (for example, 90%) to determine whether or not the final DUTY> X.

  When the final DUTY> X, the process proceeds to S14, and the limit value X is output instead of the final DUTY. That is, the minimum value of the nozzle opening is limited to the open side by limiting the maximum value of the duty to about 90%.

When the final DUTY <X, the process proceeds to S13 as usual, and the final duty (final DUTY) is output.
Thus, when the over-rotation accumulated time T exceeds the second threshold value T2, the minimum value of the nozzle opening is limited to the open side not only during transient operation but also during steady operation. That is, as shown in FIG. 7, the minimum opening is limited by providing a DUTY limit value X and controlling the duty within a range from 0% to X.

  According to the present embodiment, the turbine rotation speed detection means (S21 to S25) for directly or indirectly detecting the turbine rotation speed, and the overspeed that accumulates the time during which the turbine rotation speed exceeds a predetermined limit rotation speed. Time accumulation means (S26), and minimum opening restriction means (S31 to S34, S9 to S14) for restricting the minimum value of the nozzle opening to the open side when the accumulated time exceeds a threshold value. By providing, it is possible to prevent over-rotation that leads to high cycle fatigue without being affected by an instantaneous increase in turbine rotational speed.

  In order to prevent over-rotation, limiting the minimum value of the nozzle opening to the open side prevents over-rotation without stopping super-charging and minimizing the impact on super-charging pressure control. Can be prevented.

In particular, the reason for limiting the minimum value of the nozzle opening to the open side will be described in detail below.
In the movable nozzle vane, the pressure difference between the front and rear of the nozzle becomes large in the state of the minimum opening, thereby increasing the necessary driving force in the nozzle opening direction. In addition, the sliding resistance increases due to soot in the exhaust gas accumulated in the gap and thermal deformation over time with the minimum opening. As a result, in the state of the minimum opening, even if the negative pressure actuator is operated according to the command of the ECU, a delay occurs in the operation in the opening direction. This is considered to be the reason why the turbine speed exceeds the limit speed.

  Therefore, the minimum opening should be avoided so as not to cause an operation delay in the opening direction that causes over-rotation, i.e., so that the pressure difference before and after the nozzle is large and the minimum opening is not affected by sliding resistance. The degree is limited to the open side. That is, in the normal state, the control is performed within the range of duty 0% to 100%, but the maximum opening value is limited to, for example, 90%, and the duty is controlled within the range of duty 0% to 90%, thereby reducing the minimum opening degree. Is limited from the opening corresponding to 100% duty to the opening corresponding to 90% duty.

Thereby, although the responsiveness of the supercharging pressure control is slightly lowered, it is possible to reliably prevent the engine from being in an overspeed state while enabling the supercharging pressure control.
Further, according to the present embodiment, the minimum opening restriction means has two threshold values for the cumulative time (T1, T2), and when the cumulative time exceeds the first threshold value T1. The minimum value of the nozzle opening is limited to the open side only during transient operation during steady operation and during transient operation, and the second threshold value T2 is greater than the first threshold value T1. When the value exceeds the upper limit, the minimum value of the nozzle opening degree is limited to the open side in both the steady operation and the transient operation, so that it can be accurately controlled step by step.

  In other words, since overspeed conditions often occur in transient operation conditions, it is possible to eliminate almost all overspeeds by first taking measures in transient operation conditions. Thus, the deterioration of controllability can be made gradual.

  Further, according to the present embodiment, the minimum opening degree limiting means further includes a third threshold value T3 larger than the second threshold value T2 as a threshold value for the cumulative time, If the time exceeds the third threshold value T3, at least it will overdrive if the minimum value of the nozzle opening is limited to the open side by shifting to a safe mode that warns the driver of an abnormal state. Even if the problem persists, it can be dealt with accurately.

  Further, according to the present embodiment, the turbine rotational speed detection means detects the inlet / outlet pressure ratio PR of the intake compressor and the intake air amount Qa, and estimates the turbine rotational speed from these, This can be implemented using an existing sensor without newly adding a rotation speed sensor that directly detects the turbine rotation speed. Therefore, when it has the rotation speed sensor for turbine rotation speed detection, you may make it implement using this.

  Further, according to the present embodiment, the turbine rotational speed detection means uses the limit pressure ratio PRlimit which is the pressure ratio between the inlet and outlet of the intake compressor when the turbine rotational speed is the limit rotational speed from the actual intake air amount Qa. And determining whether or not the actual pressure ratio PR exceeds the limit pressure ratio PRlimit, thereby determining whether or not the turbine speed exceeds the limit speed, thereby obtaining the intake air amount Qa. This can be implemented simply by preparing a table that defines the limit pressure ratio PRlimit.

1 is a system diagram of an internal combustion engine with a turbocharger showing an embodiment of the present invention. Flow chart of supercharging pressure control (nozzle opening degree control) routine Over-rotation accumulated time calculation routine flowchart Over-rotation accumulated time determination routine flowchart Diagram showing the relationship between duty and nozzle opening Explanatory drawing of over-rotation judgment Illustration of minimum opening restriction

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Air cleaner 3 Intake passage 4 Variable displacement turbocharger 5 Intake compressor 6 Intercooler 7 Collector 8 Fuel injection valve 9 Exhaust passage 10 Exhaust turbine 11 Movable nozzle vane 12 Negative pressure actuator 13 for driving movable nozzle vane Negative pressure Linear solenoid valve for control 14 Air inlet 15 Reservoir tank 16 One-way valve 17 Orifice 18 Negative pressure pump 20 ECU
21 Accelerator opening sensor 22 Engine speed sensor 23 Air flow meter 24 Atmospheric pressure sensor 25 Supercharging pressure sensor 26 Gear position sensor

Claims (5)

In the turbocharger control device for an internal combustion engine that controls the supercharging pressure by controlling the nozzle opening on the inlet side of the exhaust turbine,
Turbine rotational speed detection means for detecting the turbine rotational speed;
Over-rotation time accumulating means for accumulating the time during which the turbine rotation speed exceeds a predetermined limit rotation speed;
When the cumulative time exceeds a threshold, minimum opening limit means for limiting the minimum value of the nozzle opening to the open side;
A turbocharger control device for an internal combustion engine, comprising: The minimum opening restriction means includes two thresholds for the cumulative time,
When the cumulative time exceeds the first threshold, the minimum value of the nozzle opening is limited to the open side only during transient operation during steady operation and transient operation, and the cumulative time is 2. The minimum value of the nozzle opening is limited to the open side in both steady operation and transient operation when a second threshold value greater than a threshold value of 1 is exceeded. The turbocharger control device for an internal combustion engine as described. The minimum opening restriction means further includes a third threshold value larger than the second threshold value as a threshold value for the cumulative time,
3. The turbocharger control device for an internal combustion engine according to claim 2, wherein when the accumulated time exceeds a third threshold value, a transition is made to a safe mode that warns at least an abnormal state to the driver.   4. The turbine rotation speed detection means detects a pressure ratio between an inlet and an outlet of an intake compressor and an intake air amount, and estimates the turbine rotation speed based on the detected pressure ratio. The turbocharger control device for an internal combustion engine according to claim 1.   The turbine rotation speed detection means calculates a limit pressure ratio, which is a pressure ratio between the inlet and outlet of the intake compressor when the turbine rotation speed is the limit rotation speed, from the actual intake air amount, and the actual pressure ratio is the limit. The turbocharger control device for an internal combustion engine according to claim 4, wherein it is determined whether or not a turbine rotational speed exceeds the limit rotational speed by determining whether or not a pressure ratio is exceeded. .

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