JP2006188999A - Supercharging pressure control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a supercharging pressure control device capable of quickly increasing supercharging pressure, while preventing an excessive increase in exhaust pressure (back pressure) particularly in acceleration, by properly controlling driving of a turbocharger. <P>SOLUTION: Target upstream side exhaust pressure P3CMD is calculated in response to a deviation ΔP2 between target supercharging pressure P2CMD and detected supercharging pressure P2 (S11, and S12). Limit processing of the target upstream side exhaust pressure P3CMD is performed so that the pressure ratio PR of upstream side exhaust pressure P3 to downstream side exhaust pressure P4 does not exceed the predetermined pressure ratio PR0, and the final target upstream side exhaust pressure P3CMDF is calculated (S13 to S16). Target vane opening VOCMD is set so that the detected upstream side exhaust pressure P3 coincides with the final target upstream side exhaust pressure P3CMDF (S17, and S18). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a supercharging pressure control device for an internal combustion engine equipped with a turbocharger.

  A compressor wheel that pressurizes the air sucked into the internal combustion engine, a turbine wheel that is connected to the compressor wheel and rotationally driven by the kinetic energy of the exhaust gas, and is opened and closed to change the flow rate of the exhaust gas blown to the turbine wheel Variable capacity turbochargers having a variable vane to be driven are widely known.

  Patent Document 1 discloses a control device that controls the opening degree of a variable vane of such a turbocharger. In this control device, when the detected supercharging pressure is lower than the target supercharging pressure, the variable vane is controlled in the closing direction, and when the detected supercharging pressure is higher than the target supercharging pressure, the variable vane opens. Controlled in direction. If the increase in supercharging pressure is not detected when the variable vane is controlled in the closing direction, the variable vane is forcibly controlled in the opening direction. This prevents the exhaust pressure (back pressure) on the upstream side of the turbine from increasing excessively and causing a decrease in engine output, particularly when the engine speed is high.

Japanese Patent Laid-Open No. 10-331648

  The increase in supercharging pressure when the variable vane is controlled in the closing direction is greatly delayed compared to the increase in exhaust pressure, so it is confirmed that no increase in supercharging pressure is detected, and then the variable vane is controlled in the opening direction. Then, the control timing in the opening direction is delayed, the exhaust pressure is excessively increased, and the engine output may be decreased.

  The present invention has been made paying attention to this point, and appropriately controls the flow rate of the exhaust gas that contributes to the rotational drive of the turbine wheel to prevent an excessive increase in the exhaust pressure (back pressure) particularly during acceleration. It is another object of the present invention to provide a supercharging pressure control device that can quickly increase the supercharging pressure.

  In order to achieve the above object, an invention according to claim 1 is directed to a compressor wheel (15) that pressurizes air sucked into an internal combustion engine (1), and the kinetic energy of exhaust gas of the engine connected to the compressor wheel. Internal combustion engine comprising a turbocharger (8) having a turbine wheel (10) driven to rotate by an exhaust gas, and an exhaust gas flow rate varying means (12) for changing the flow rate of exhaust gas blown to the turbine wheel (10) In the supercharging pressure control apparatus, the first exhaust pressure detection means (23) for detecting the exhaust pressure (P3) on the upstream side of the turbine wheel (10), and the exhaust pressure on the downstream side of the turbine wheel (10) ( The pressure ratio (PR = P3 / P) of the second exhaust pressure detecting means (24) for detecting P4) and the upstream exhaust pressure (P3) to the downstream exhaust pressure (P4). ) So as not to exceed a predetermined pressure ratio (PR0), characterized in that it comprises a control means for the control of the exhaust gas flow rate changing means (12).

  The control operation of the control means is to control the exhaust gas flow rate varying means so that the pressure ratio (P4 / P3) of the downstream exhaust pressure to the upstream exhaust pressure does not fall below the predetermined pressure ratio. It goes without saying that they are equivalent.

The exhaust gas flow rate varying means is preferably a variable vane that is driven to open and close to change the flow rate of the exhaust gas blown to the turbine wheel. And the said control means sets the target supercharging pressure (P2CMD) according to the driving | running state of the said engine, and the detected supercharging pressure (P2) is the said target supercharging pressure (P2CMD). Target upstream exhaust pressure setting means for setting the target upstream exhaust pressure (P3CMD) so as to coincide with P2CMD), and the detected upstream exhaust pressure (P3) coincides with the target upstream exhaust pressure (P3CMD). It is desirable to control the opening degree (VO) of the variable vane. Then, the target upstream exhaust pressure setting means calculates an upstream limit value (P3LMT) by multiplying the detected downstream exhaust pressure (P4) by the predetermined pressure ratio (PR0), and the upstream limit value is calculated. It is desirable to set the target upstream exhaust pressure (P3CMDF) so as not to exceed the value (P3LMT).
Thus, by adopting cascade control including two feedback controls, control performance can be improved.

  According to the first aspect of the present invention, the exhaust gas flow rate varying means is controlled so that the pressure ratio of the upstream exhaust pressure to the downstream exhaust pressure of the turbine wheel does not exceed the predetermined pressure ratio. In general, when the pressure ratio increases, the mass flow rate of exhaust gas that drives the turbine wheel (hereinafter simply referred to as “turbine exhaust gas flow rate”) increases. However, when the exhaust gas flow rate exceeds the pressure ratio PR0 that reaches the sonic speed, Does not increase. Therefore, by setting the predetermined pressure ratio in the vicinity of the pressure ratio PR0, for example, when the engine is accelerated, the exhaust gas flow rate through the turbine is rapidly increased without excessively increasing the upstream exhaust pressure, and the supercharging pressure is quickly increased. Can be increased.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention. An internal combustion engine (hereinafter referred to as “engine”) 1 is a diesel engine that directly injects fuel into a cylinder, and a fuel injection valve 9 is provided in each cylinder. The fuel injection valve 9 is electrically connected to an electronic control unit (hereinafter referred to as “ECU”) 20, and the valve opening time of the fuel injection valve 9 is controlled by the ECU 20.

  The engine 1 includes an intake pipe 2, an exhaust pipe 4, and a turbocharger 8. The turbocharger 8 includes a turbine 11 having a turbine wheel 10 that is rotationally driven by kinetic energy of exhaust, and a compressor 16 having a compressor wheel 15 connected to the turbine wheel 10 via a shaft 14. The compressor wheel 15 pressurizes (compresses) air sucked into the engine 1.

  The turbine 11 has a plurality of variable vanes 12 (only two are shown) that are driven to change the flow rate of exhaust gas blown to the turbine wheel 10, and an actuator (not shown) that drives the variable vanes to open and close. By changing the opening VO of the variable vane 12 (hereinafter referred to as “vane opening”), the flow rate of the exhaust gas blown to the turbine wheel 10 can be changed, and the rotational speed of the turbine wheel 10 can be changed. It is configured. The actuator that drives the variable vane 12 is connected to the ECU 20, and the vane opening VO is controlled by the ECU 20. More specifically, the ECU 20 supplies a control signal with a variable duty ratio to the actuator, thereby controlling the vane opening VO. The configuration of a turbocharger having a variable vane is widely known, and is disclosed in, for example, Japanese Patent Laid-Open No. 1-208501.

  Between the exhaust pipe 4 and the intake pipe 2, an exhaust gas recirculation passage 5 that circulates exhaust gas to the intake pipe 2 is provided. The exhaust gas recirculation passage 5 is provided with an exhaust gas recirculation valve (hereinafter referred to as “EGR valve”) 6 for controlling the exhaust gas recirculation amount. The EGR valve 6 is an electromagnetic valve having a solenoid, and the valve opening degree is controlled by the ECU 20. The EGR valve 6 is provided with a lift sensor 7 for detecting the valve opening degree (valve lift amount) LACT, and the detection signal is supplied to the ECU 20. An exhaust gas recirculation mechanism is configured by the exhaust gas recirculation passage 5 and the EGR valve 6.

  The intake pipe 2 is provided with an intake air flow rate sensor 21 that detects an intake air flow rate GA and a supercharging pressure sensor 22 that detects an intake pressure (supercharging pressure) P2 on the downstream side of the compressor 16. Further, the exhaust pipe 4 is provided with a first exhaust pressure sensor 23 for detecting the exhaust pressure P3 upstream of the turbine 11 and a second exhaust pressure sensor 24 for detecting the exhaust pressure P4 downstream of the turbine 11. Yes. These sensors 21 to 24 are connected to the ECU 20, and detection signals from the sensors 21 to 24 are supplied to the ECU 20.

A particulate matter filter (hereinafter referred to as “DPF”) 17 that collects particulate matter (mainly made of soot) contained in the exhaust gas is provided on the exhaust pipe 4 downstream of the second exhaust pressure sensor 24. It has been.
An accelerator sensor 25 that detects a depression amount (hereinafter referred to as “accelerator pedal operation amount”) AP of an accelerator pedal (not shown) of a vehicle driven by the engine 1 and an engine rotation that detects an engine speed (rotation speed) NE. A number sensor 26 is connected to the ECU 20, and detection signals from these sensors are supplied to the ECU 20.

  The ECU 20 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, a central processing unit (hereinafter referred to as “CPU”). A storage circuit for storing various calculation programs executed by the CPU and calculation results, an actuator for driving the variable vane 12 of the turbine 11, an output circuit for supplying a drive signal to the fuel injection valve 9, the EGR valve 6, etc. Consists of

  The ECU 20 calculates the target boost pressure P2CMD according to the operating state of the engine 1, specifically, the accelerator pedal operation amount AP and the engine speed NE, and the detected boost pressure P2 matches the target boost pressure P2CMD. Thus, the supercharging pressure control for controlling the vane opening VO is performed. Further, the ECU 20 calculates the valve opening time TOUT of the fuel injection valve 9 according to the accelerator pedal operation amount AP and the engine speed NE, and supplies a drive signal corresponding to the valve opening time TOUT to the fuel injection valve 9. The ECU 20 further sets a target intake air amount GACMD according to the accelerator pedal operation amount AP and the engine speed NE, determines an exhaust gas recirculation amount based on the target intake air amount GACMD and the detected intake air flow rate GA, The lift amount (valve opening amount) of the EGR valve 6 is controlled.

In order to quickly increase the supercharging pressure, it is necessary to increase the mass flow rate GEtbn of the exhaust gas passing through the turbine 11. Therefore, the turbine 11 is modeled as a nozzle as shown in FIG.
The mass flow rate GEtbn of the exhaust gas passing through the nozzle can be expressed by the following formula (1).
GEtbn = Atbn (VO) .U (P3) .Φ (P4 / P3) (1)

  Here, Atbn is a turbine effective opening area defined as a function of the vane opening VO, U (P3) is an upstream condition function calculated by the following equation (2), and Φ (P4 / P3) is These are pressure functions given by the following equations (3) and (4). P3 and P4 are an upstream exhaust pressure and a downstream exhaust pressure, respectively. Ρ in equation (2) is the density of exhaust gas passing through the nozzle, and κ in equations (3) and (4) is the specific heat ratio of exhaust gas passing through the nozzle. When the exhaust gas flow velocity is lower than the sonic velocity, the equation (3) is applied, and when the exhaust gas flow velocity is equal to or higher than the sonic velocity, the equation (4) is applied.

ここで、圧力比ＰＲを
ＰＲ＝Ｐ３／Ｐ４ （５）
と定義すると、圧力関数Φは圧力比ＰＲの関数として、図３に示すように変化する。図３のＰＲ０は、下記式（６）により算出される所定圧力比である。式（６）の右辺は、式（３）に含まれる右側の不等式の右辺の式の逆数に相当する。

Here, the pressure ratio PR is PR = P3 / P4 (5)
, The pressure function Φ changes as shown in FIG. 3 as a function of the pressure ratio PR. PR0 in FIG. 3 is a predetermined pressure ratio calculated by the following equation (6). The right side of Expression (6) corresponds to the reciprocal of the expression on the right side of the right inequality included in Expression (3).

  That is, the pressure function Φ increases as the pressure ratio PR increases, but becomes constant when the exhaust gas flow velocity exceeds a predetermined pressure ratio PR0 at which the sonic velocity is reached (equation (4) is applied). Accordingly, the mass flow rate GEtbn changes, for example, as shown by a curve L3 in FIG. 4, and hardly increases when the pressure ratio PR exceeds the predetermined pressure ratio PR0. The curves L1 and L3 in FIG. 4 correspond to the state where the vane opening degree VO is maximum and the minimum, and the curve L2 corresponds to an intermediate state between them. The range in which the curves L1 and L2 are drawn is narrowed because the pressure ratio PR does not increase to a certain extent as the vane opening VO increases.

  In consideration of the characteristics shown in FIG. 4, in this embodiment, when it is necessary to quickly increase the supercharging pressure as in the acceleration of the engine, the vane opening VO is initially reduced (when the engine is running at a low speed). Then, the pressure ratio PR is increased, and thereafter, the vane opening degree VO is controlled to be gradually increased so that the pressure ratio PR does not exceed the predetermined pressure ratio PR0. As a result, the supercharging pressure can be quickly increased without excessively increasing the upstream side exhaust pressure P3 of the turbine 11.

  The predetermined pressure ratio PR0 can be theoretically obtained from the specific heat ratio of the exhaust gas, but is actually set to a value determined by experiment, for example, a value between 1.9 and 2.5. ing.

  FIG. 5 is a block diagram illustrating a configuration of a supercharging pressure control module that performs the above-described control. The function of each block is realized by calculation by the CPU of the ECU 20.

  The supercharging pressure control module shown in FIG. 5 includes a P2CMD setting unit 31, a subtractor 32, a P2 controller 33, a limiter 34, a subtractor 35, and a P3 controller 36. The P2CMD setting unit 31 sets a target boost pressure P2CMD according to the engine speed NE and the target fuel amount QCMD. Here, the target fuel amount QCMD is a target value of the fuel amount supplied to the engine 1 and is set so as to increase as the accelerator pedal operation amount AP increases. The target boost pressure P2CMD is set to increase as the engine speed NE increases and as the target fuel amount QCMD increases. Therefore, at the time of acceleration at which the accelerator pedal is depressed, the target boost pressure P2CMD increases stepwise. The subtracter 32 subtracts the detected supercharging pressure P2 from the target supercharging pressure P2CMD to calculate a supercharging pressure deviation ΔP2.

  The P2 controller 33 calculates the target upstream side exhaust pressure P3CMD according to the supercharging pressure deviation ΔP2. More specifically, the target upstream side exhaust pressure P3CMD is calculated so that the supercharging pressure deviation ΔP2 becomes “0” by, for example, PID (proportional integral derivative) control. That is, the P2 controller 33 increases the target upstream exhaust pressure P3CMD when ΔP2> 0, and decreases the target upstream exhaust pressure P3CMD when ΔP2 <0.

  The limiter 34 calculates an upstream limit value P3LMT by multiplying the detected downstream exhaust pressure P4 by a predetermined pressure ratio PR0. When the target upstream exhaust pressure P3CMD is equal to or lower than the upstream limit value P3LMT, the target upstream exhaust pressure P3CMD is directly used as the final target upstream exhaust pressure P3CMDF, while the target upstream exhaust pressure P3CMD is the upstream limit value. When P3LMT is exceeded, the upstream limit value P3LMT is set as the final target upstream exhaust pressure P3CMDF. The subtractor 35 subtracts the upstream exhaust pressure P3 detected from the final target upstream exhaust pressure P3CMDF to calculate an exhaust pressure deviation ΔP3.

  The P3 controller 36 calculates the target vane opening degree VOCMD according to the exhaust pressure deviation ΔP3. More specifically, the target vane opening degree VOCMD is calculated by, for example, PID control so that the exhaust pressure deviation ΔP3 becomes “0”. That is, the P3 controller 36 decreases the target vane opening VOCMD when ΔP3> 0, and increases the target vane opening VOCMD when ΔP3 <0.

FIG. 6 is a flowchart of the supercharging pressure control process for realizing the functions of the functional blocks shown in FIG. This process is executed every predetermined time by the CPU of the ECU 20.
In step S10, the target boost pressure P2CMD is set according to the engine speed NE and the target fuel amount QCMD. In step S11, the detected boost pressure P2 is subtracted from the target boost pressure P2CMD to calculate the boost pressure deviation ΔP2. In step S12, the target upstream exhaust pressure P3CMD is calculated using, for example, PID control so that the supercharging pressure deviation ΔP2 becomes “0”. In step S13, an upstream limit value P3LMT is calculated by multiplying the detected downstream exhaust pressure P4 by a predetermined pressure ratio PR0. Next, it is determined whether or not the target upstream exhaust pressure P3CMD calculated in step S12 is larger than the upstream limit value P3LMT (step S14).

  If P3CMD ≦ P3LMT in step S14, the final target upstream exhaust pressure P3CMDF is set to the target upstream exhaust pressure P3CMD (step S16). If P3CMD> P3LMT, the final target upstream exhaust pressure P3CMDF is set to the upstream limit value P3LMT (step S15). Through steps S13 to S16, the final target upstream exhaust pressure P3CMDF is set so that the pressure ratio PR does not exceed the predetermined pressure ratio PR0.

  In step S17, the exhaust pressure deviation ΔP3 is calculated by subtracting the upstream exhaust pressure P3 detected from the final target upstream exhaust pressure P3CMDF. In step S18, the target vane opening degree VOCMD is calculated using, for example, PID control so that the exhaust pressure deviation ΔP3 becomes “0”. In step S19, the actuator of the variable vane 12 is driven so that the vane opening VO matches the target vane opening VOCMD.

  FIG. 7 is a time chart for explaining the supercharging pressure control shown in FIG. 6 and shows the vane opening VO, the pressure ratio PR, and the supercharging pressure P2 when the accelerator pedal is greatly depressed at time t0. Shows the transition. In addition, the broken line shown to FIG.7 (b) and (c) shows the characteristic when the limit process of pressure ratio PR is not performed.

  The vane opening VO decreases stepwise to the minimum opening VOMIN at time t0, and is maintained at the minimum opening VOMIN until time t1 when the pressure ratio PR reaches the predetermined pressure ratio PR0. After time t1, the vane opening degree VO increases, and the pressure ratio PR is maintained substantially at the predetermined pressure ratio PR0. Thereby, the supercharging pressure P2 can be increased more rapidly than in the case where the limit process of the pressure ratio PR is not performed.

  Further, the downstream exhaust pressure P4 is detected by the second exhaust pressure sensor 24 immediately downstream of the turbine 11 (upstream of the DPF 17), and the limit process of the pressure ratio PR is performed in accordance with the detected downstream exhaust pressure P4. Therefore, accurate control can be performed even if the soot accumulation state in the DPF 17 changes.

  In the present embodiment, the variable vane 12 and the actuator that drives the variable vane 12 correspond to exhaust gas flow rate variable means, the first exhaust pressure sensor 23 corresponds to first exhaust pressure detection means, and the second exhaust pressure sensor 24 corresponds to This corresponds to the second exhaust pressure detection means. Moreover, ECU20 comprises a control means. Specifically, the process shown in FIG. 6 corresponds to the control means, step S10 corresponds to the target boost pressure setting means, and steps S12 to S15 correspond to the target upstream side exhaust pressure setting means.

  The present invention is not limited to the embodiment described above, and various modifications can be made. For example, the downstream side exhaust pressure P4 may be calculated by detecting the atmospheric pressure PA with an atmospheric pressure sensor and adding the correction amount ΔP to the detected atmospheric pressure PA. Since the DPF is provided on the downstream side of the turbine 11 as in the present embodiment and the NOx absorption catalyst for purifying NOx is provided, the downstream exhaust pressure P4 is slightly higher than the atmospheric pressure PA. . Accordingly, a correction amount ΔP to be added to the atmospheric pressure PA is obtained in advance, and the downstream exhaust pressure P4 (approximate value) is simply obtained by adding the correction amount ΔP to the detected atmospheric pressure PA. Can do. In this case, the atmospheric pressure sensor and the ECU 20 constitute a second exhaust pressure detection means. Thereby, it is not necessary to provide the second exhaust pressure sensor, and the configuration can be simplified.

Further, in the above-described embodiment, the example in which the present invention is applied to the supercharging pressure control in the internal combustion engine including the turbocharger having the variable vane has been shown. It is also applicable to.
(1) A turbocharger having a fixed capacity, a bypass passage that bypasses the turbine of the turbocharger, and a wastegate valve provided in the bypass passage, and by changing the opening of the wastegate valve, A control device configured to control a supercharging pressure by changing an exhaust amount flowing into a turbine. In this case, the bypass passage and the wastegate valve correspond to the exhaust gas flow rate varying means.
(2) A turbocharger having a fixed capacity is provided, and the supercharging pressure is controlled by changing the exhaust amount of the internal combustion engine according to the engine operating state (for example, the engine speed and the target fuel amount). Control unit. In this control device, the exhaust amount is changed by changing the amount of fuel supplied to the internal combustion engine or the amount of intake air, for example. In this case, the control unit for controlling the exhaust amount corresponds to the exhaust gas flow rate varying means.

In the above-described embodiment, the P2 controller 33 and the P3 controller 36 set the control deviation to “0” by PID control. However, the present invention is not limited to this, and sliding mode control based on modern control theory or A controller that performs adaptive control may be used.
In the above-described embodiment, an example is shown in which the present invention is applied to the supercharging pressure control of the diesel internal combustion engine of the present invention. However, the present invention is also applicable to supercharging pressure control of a gasoline internal combustion engine.
The present invention can also be applied to supercharging pressure control of a marine vessel propulsion engine such as an outboard motor having a vertical crankshaft.

It is a figure which shows the structure of the internal combustion engine and its control apparatus concerning one Embodiment of this invention. It is a figure which shows the shape of a general nozzle. It is a figure which shows the relationship between ratio (PR) of the pressure (P3) of the upstream of a nozzle, and the pressure (P4) of a downstream, and the value of a pressure function ((PHI)). It is a figure which shows the relationship between a pressure ratio (PR) and the mass flow rate (GEtbn) of the exhaust gas which passes a turbine. It is a block diagram for demonstrating the function of the module which performs supercharging pressure control. It is a flowchart of a supercharging pressure control process. It is a figure for demonstrating the supercharging pressure control in this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 8 Turbocharger 10 Turbine wheel 11 Turbine 12 Variable vane (exhaust gas flow variable means)
15 Compressor wheel 16 Compressor 20 Electronic control unit (control means)
22 Supercharging pressure sensor 23 First exhaust pressure sensor (first exhaust pressure detecting means)
24 Second exhaust pressure sensor (second exhaust pressure detection means)

Claims (1)

A turbocharger having a compressor wheel for pressurizing air sucked into the internal combustion engine, a turbine wheel connected to the compressor wheel and driven to rotate by the kinetic energy of the exhaust gas of the engine, and exhaust blown to the turbine wheel In a supercharging pressure control device for an internal combustion engine provided with an exhaust gas flow rate variable means for changing a gas flow rate,
First exhaust pressure detection means for detecting an exhaust pressure upstream of the turbine wheel;
Second exhaust pressure detecting means for detecting exhaust pressure downstream of the turbine wheel;
And a control means for controlling the exhaust gas flow rate varying means so that the pressure ratio of the upstream side exhaust pressure to the downstream side exhaust pressure does not exceed a predetermined pressure ratio. .

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