DE102017125363B4 - Control device for an internal combustion engine - Google Patents

Abstract

Control device for an internal combustion engine, the internal combustion engine comprising a turbocharger (20) and an exhaust gas recirculation system (30), the turbocharger comprising a turbine (20b) with a variable nozzle (22), the exhaust gas recirculation system (30) having an EGR duct (32), which connects a portion of an exhaust passage upstream of the turbine to an intake passage, and the EGR passage (32) has an EGR valve (36), the control device comprising: means for sensing a current value (Pds) of a downstream turbine pressure, which is an exhaust port internal pressure at an exhaust side of the turbine; means for detecting a current value (Pim) of an intake passage pressure, which is a pressure within a space of the intake passage which is connected to the EGR passage; means for detecting a current value (Tus) an upstream-side turbine temperature which is an exhaust passage inside temperature at an inlet side of the turbine; center l for detecting a current value (θegr) of an opening of the EGR valve; means for detecting a current value (θvn) of a degree of closure of the variable nozzle; means for detecting a current value (Gadly) of a fresh air amount which is a flow rate of fresh air, which is brought into the intake passage; means for calculating a current value (Gcyl) of an amount of gas within a cylinder based on a pressure and a temperature of gas supplied to the cylinder; means for calculating a current value (Gf) of a fuel flow rate of a fuel injection valve ; Means for calculating a current value (Mtb) of a turbine flow rate, which is a flow rate of the gas flowing through the turbine, based on the current value (Gadly) of the fresh air amount and the current value (Gf) of the fuel flow rate; means for calculating a current one Value (Megr) of an EGR valve flow rate based on a difference between a Total sum of the current value (Gcyl) of the amount of gas within the cylinder and the current value (Gf) of the fuel flow rate and the current value (Mtb) of the turbine flow rate; means for storing a previous value (Pus_0) of the upstream turbine pressure, which is the internal exhaust port pressure on the inlet side of the turbine; means for pre-storing a map of an effective turbine opening area, which associates an effective turbine opening area of the entire turbine including the variable nozzle with the turbine flow rate and the degree of closure of the variable nozzle; means for reading out an effective turbine opening area (µAtb) according to the current value (Mtb ) the turbine flow rate and the current value (θvn) of the degree of closure of the variable nozzle from the map of the effective turbine opening area; means for pre-storing a map of an effective EGR valve opening area, which is an effective EGR valve opening area of the entire A. Gas recirculation system including the EGR valve associated with the EGR valve flow rate and the opening of the EGR valve; means for reading out an effective EGR valve opening area (µAegr) according to the current value (Megr) of the EGR valve flow rate and the current value (θegr) of the opening of the EGR valve from the map of the effective EGR valve opening area; means for pre-storing a first coefficient map if a function (Φ) of a pressure ratio (π) between a downstream pressure and an upstream pressure of the nozzle , which is defined by equation 1, is divided into a plurality of segments of the pressure ratio (π) by a piecewise linear method and is linearly approximated for each segment of the pressure ratio (π) by a linear function which is defined by equation 2, wherein the first coefficient map coefficients (a, b) of the linear function which for each of the segments of the pressure ratio (π), associated with the segments of the pressure ratio (π), where (π) = κκ − 1 ∗ (π2κ − πκ + 1κ) and equation 2Φ (π) = a ∗ π +; means of reading of each of the coefficients (a, b) corresponding to the segment which is relevant to the pressure ratio (π) from the first coefficient map, if a ratio between the current value (Pds) of the downstream turbine pressure and the previous value (Pus_0) of the upstream Turbine pressure is used as the pressure ratio (π) in equation 2; means for pre-storing a second coefficient map which combines coefficients (c, d) of the linear function defined for each of the segments of the pressure ratio (π) with the segments of the pressure ratio ( π), associated when the function (Φ) of the pressure ratio (π) between the downstream side pressure and the upstream side pressure of the nozzle, which is defined by equation 1, is divided into a plurality of segments of the Pressure ratio (π) is divided by a piece-wise linear method and for each segment of the pressure ratio (π) is linearly approximated by a linear function defined by Equation 3, where (π) = c ∗ π + dist; means for reading out each of the coefficients (c, d) corresponding to the segment relevant to the pressure ratio (π) from the second coefficient map when a ratio between the current value (Pim) of the intake manifold pressure and the previous value (Pus_0) of the upstream turbine pressure as the pressure ratio (π) is used in equation 3; means for calculating the current value (Pus) of the upstream turbine pressure by equation 4 based on the current value (Pds) of the downstream turbine pressure, the current value (Pim) of the intake manifold pressure, the current value (Tus) the upstream turbine temperature, a total of the current value (Gcyl) of the amount of gas within the cyli nders and the current value (Gf) of the fuel flow rate, the effective turbine opening area (µAtb), the effective EGR valve opening area (µAegr) and each of the coefficients (a, b, c, d), wherePus = (Gcyl + Gf) ∗ R ∗ Tus2 − μAegr ∗ Pim ∗ c − μAtb ∗ Pds ∗ aμAegr ∗ d + μAtb ∗ bist; andmeans for controlling the internal combustion engine based on the current value (Pus) of the turbine upstream pressure.

Description

BACKGROUND OF THE INVENTION

Field of invention

The present invention relates to a control device which controls an internal combustion engine having a turbocharger and an exhaust gas recirculation (EGR) system, the turbocharger having a turbine with a variable nozzle.

Description of the prior art

In JP 2014-047717 A discloses a method for calculating an orifice area of a variable nozzle, the orifice area being needed to achieve a target pressure within an exhaust manifold. According to the procedure described in the JP 2014-047717 A disclosed, a pressure Pwg on a downstream side of an EGR valve, a pressure Peg on an upstream side of the EGR valve and a temperature Teg on the upstream side of the EGR valve are detected by sensors, respectively. A pressure ratio between the pressure Pwg on the downstream side of the EGR valve and the pressure Peg on the upstream side of the EGR valve is calculated with an equation based on Bernoulli's theorem. Based on the temperature Teg on the upstream side of the EGR valve and the opening area calculated from an EGR valve opening VTegr, an EGR circulation amount Geg, which is a flow rate of EGR gas flowing through the EGR valve, is calculated.

According to the procedure described in the JP 2014-047717 A is then disclosed, a working gas amount Gwg, which is a flow rate of a working gas supplied to a cylinder, is calculated based on an intake air temperature Tin and an intake air pressure Pwg which are detected by sensors. By subtracting the EGR circulation amount Geg from the working gas amount Gwg, a flow rate Gti of an exhaust gas flowing into the turbine is calculated. A turbine outlet pressure Pte and a turbine inlet temperature Tti are each calculated based on relevant state variables. Then, based on a target pressure Pme in the exhaust manifold, the turbine outlet pressure Pte, and the turbine inlet temperature Tti, a required opening area Ane of the variable nozzle is calculated with the equation based on Bernoulli's theorem.

JP 2016-065484 A discloses an upstream throttle pressure estimator and provides piece-wise linear interpolation of the flow characteristic of a throttle.

SUMMARY OF THE INVENTION

Using the equation based on Bernoulli's theorem, as in FIG JP 2014-047717 A is disclosed, the pressure in the exhaust manifold, that is, an estimated value of the upstream turbine pressure, may be calculated based on the opening of the variable nozzle. The calculation requires a turbine flow rate, which is a flow rate of the exhaust gas flowing through the turbine. In the procedure described in the JP 2014-047717 A is disclosed, the turbine flow rate is calculated based on the amount of working gas within the cylinder and the EGR circulation amount. According to the procedure described in the JP 2014-047717 A is disclosed, the EGR circulation amount is calculated based on a pressure ratio between the pressures before and after the EGR valve. In this case, the calculation requires a sensor that measures the pressure on the downstream side of the EGR valve and a sensor that measures the pressure on the upstream side of the EGR valve. However, from a viewpoint of reducing the number of parts, it is preferable to reduce the number of sensors as much as possible.

If the turbine upstream pressure can be obtained through a calculation as described above, the EGR valve upstream pressure can also be calculated from the turbine upstream pressure. Therefore, the need for the sensor for measuring the pressure on the upstream side of the EGR valve can be eliminated. In this case, however, the EGR circulation amount cannot be calculated based on the pressure ratio between the pressures before and after the EGR valve. Accordingly, the turbine flow rate must be calculated using a method that differs from that in the JP 2014-047717 A disclosed method differs.

One obvious method is to calculate the turbine flow rate from an amount of fresh air measured with an air flow sensor. The turbine flow rate has a response delay relative to the amount of fresh air, the response delay corresponding to the time it takes for the gas to reach the turbine after passing through the air flow sensor. If delayed processing is applied to the fresh air amount in consideration of the response delay, the turbine flow rate can be calculated. However, since noise tends to be superimposed on readings from the air flow sensor, it is difficult to accurately calculate the turbine upstream pressure based on the turbine flow rate calculated from the amount of fresh air measured by the air flow sensor.

The present invention provides a control device for an internal combustion engine capable of accurately calculating the turbine upstream pressure which is an exhaust passage internal pressure on an intake side of the turbine.

The control device for an internal combustion engine according to the present invention is configured to control the internal combustion engine including a turbocharger and an EGR system, the turbocharger including a turbine with a variable nozzle, the EGR system having an EGR passage which connects a portion of an exhaust passage upstream of the turbine to an intake passage, and the EGR passage has an EGR valve. The control device is configured to perform the following processing.

The control device detects the following state variables directly or indirectly with sensors. The state quantities include: a current value Pds of a downstream turbine pressure, which is an exhaust passage internal pressure on an exhaust side of the turbine; a current value Pim of an intake passage pressure, which is a pressure within the space of the EGR passage connected to the intake passage; a current value Tus of an upstream-side turbine temperature, which is an exhaust passage internal temperature on an intake side of the turbine; a current value θegr of an opening of the EGR valve; a current value θvn of a degree of closure of the variable nozzle; and a current value Gadly of a fresh air amount, which is a flow rate of fresh air brought into the intake passage.

The control device acquires the following state quantities by calculation. The state variables include: a current value Gcyl of an amount of gas within the cylinder, which is calculated from a pressure and a temperature of a gas supplied to the cylinder; a current value Gf of a fuel flow rate of a fuel injection valve; a current turbine flow rate value Mtb, which is a flow rate of the gas flowing through the turbine, which is calculated based on the current value Gadly of the fresh air amount and the current value Gf of the fuel flow rate; and a current value Megr of an EGR valve flow rate calculated based on a difference between the sum total of the current value Gcyl of the amount of gas within the cylinder and the current value Gf of the fuel flow rate and the current value Mtb of the turbine flow rate.

The control device temporarily stores a previous value Pus_0 of the upstream turbine pressure, which is the exhaust port internal pressure on the inlet side of the turbine.

The control device pre-stores an effective turbine opening area map which associates an effective turbine opening area of the turbine having the variable nozzle, which is regarded as a single nozzle, with the turbine flow rate and the degree of closure of the variable nozzle. The control device pre-stores an EGR valve effective opening area map which associates an EGR valve effective opening area of the EGR valve, which is regarded as a single nozzle, with the EGR valve flow rate and the opening of the EGR valve .

The control device reads out an effective turbine opening area μAtb from the map of the effective turbine opening area, which corresponds to the current value Mtb of the turbine flow rate and the current value θvn of the degree of closure of the variable nozzle. The control device also reads from the map of the effective EGR valve opening area an effective EGR valve opening area μAegr, which corresponds to the current value Megr of the EGR valve flow rate and the current value θegr of the opening of the EGR valve.

$$\mathrm{\Phi }\left(\pi \right)=a\mathrm{\ast }\pi +b$$

When a function Φ of a pressure ratio π between the downstream side pressure and the upstream side pressure of the nozzle, which is defined by Equation 1, is divided into a plurality of segments of the pressure ratio π and for each segment of the pressure ratio π by a linear Function defined by equation 2 is linearly approximated, the control device pre-stores a first coefficient map which associates coefficients a, b of the linear function defined for each of the segments of the pressure ratio π with the segments of the pressure ratio π. $$\mathrm{\Phi }\left(\pi \right)=\sqrt{\frac{\kappa }{\kappa -1}\mathrm{\ast }\left({\mathrm{<figure-callout\; id="2"\; label="\pi "\; filenames="DE102017125363B4\_0019.png,DE102017125363B4\_0020.png"\; state="\{\{state\}\}">\pi </figure-callout>}}^{\frac{2}{\kappa }}-{\pi }^{\frac{\kappa +1}{\kappa }}\right)}$$

$$\mathrm{\Phi }\left(\pi \right)=a\mathrm{\ast }\pi +b$$

If the function Φ of the pressure ratio π between the downstream side pressure and the upstream side pressure of the nozzle, which is defined by Equation 1, is divided into a plurality of segments of the pressure ratio π by a piecewise linear method, and for each segment of the pressure ratio π by a linear one Function defined by equation 3 is linearly approximated, the control device pre-stores a second coefficient map which associates coefficients c, d of the linear function defined for each of the segments of the pressure ratio π with the segments of the pressure ratio π. $$\mathrm{\Phi }\left(\pi \right)=c\mathrm{\ast }\pi +d$$

If a ratio between the current value Pds of the downstream-side turbine pressure and the previous value Pus_0 of the upstream-side turbine pressure is used as the pressure ratio π in Equation 2, the control device reads each of the coefficients a, b corresponding to the segment relevant to the pressure ratio π from the first coefficient map out. If a ratio between the current value Pim of the intake manifold pressure and the previous value Pus_0 of the upstream-side turbine pressure is used as the pressure ratio π in Equation 3, the control device reads out each of the coefficients c, d corresponding to the segment relevant to the pressure ratio π from the second coefficient map .

Based on the current value Pds of the downstream turbine pressure, the current value Pim of the intake manifold pressure, the current value Tus of the upstream turbine temperature, the total sum of the current value Gcyl of the gas amount within the cylinder and the current value Gf of the fuel flow rate, the effective turbine opening area µAtb, the effective EGR valve opening area µAegr and each of the coefficients a, b, c, d, the control device calculates a current value Pus of the upstream turbine pressure by equation 4: $$Pus=\frac{\left(Gcyl+Gf\right)\mathrm{\ast }\sqrt{\frac{\mathrm{R.}\mathrm{\ast }Tus}{2}}-\mu \mathrm{A.}eGr\mathrm{\ast }Pim\mathrm{\ast }c-\mu \mathrm{A.}tb\mathrm{\ast }Pds\mathrm{\ast }a}{\mu \mathrm{A.}eGr\mathrm{\ast }d+\mu \mathrm{A.}tb\mathrm{\ast }b}$$

The control device controls the engine based on the current value Pus of the upstream-side turbine pressure calculated based on the above logic.

According to the control device, the turbine upstream pressure can be calculated accurately by using Equation 4. Therefore, the engine can be controlled based on the accurate turbine upstream pressure. Since the turbine flow rate used for calculating the effective turbine opening area is calculated based on the amount of fresh air, the influence of a dispersion in the measurement values of the amount of fresh air caused by noise is applied to the calculation value of the effective turbine opening area. Similarly, since the EGR valve flow rate used for calculating the effective EGR valve opening area is also calculated using the fresh air amount, the influence of a dispersion in the measurements of the fresh air amount caused by noise becomes , applied to the calculated value of the effective EGR valve opening area. However, according to the relationship between the effective turbine opening area and the turbine flow rate, the sensitivity of the effective turbine opening area to the dispersion in the turbine flow rate is not high. Similarly, according to the relationship between the effective EGR valve opening area and the EGR valve flow rate, the The sensitivity of the effective EGR valve opening area to the dispersion in the EGR valve flow rate is also not high. Therefore, the dispersion in the measured values of the amount of fresh air due to noise has a limited influence on the calculation results of the effective turbine opening area and the effective EGR valve opening area. Accordingly, the calculation accuracy of the upstream-side turbine pressure, which includes the effective turbine opening area and the effective EGR valve opening area as parameters, is sufficiently ensured.

Figure list

• 1 die schematische Konfiguration eines Verbrennungsmotors, an welchem eine Steuerungsvorrichtung einer Ausführungsform der vorliegenden Erfindung angewandt wird, veranschaulicht;
• 2 die Beziehung zwischen dem Schließgrad einer variablen Düse, einer Turbinendurchflussrate und einer wirksamen Turbinenöffnungsfläche veranschaulicht;
• 3 die Beziehung zwischen der Öffnung eines EGR-Ventils, einer EGR-Ventil-Durchflussrate und einer wirksamen EGR-Ventil-Öffnungsfläche veranschaulicht;
• 4 eine Funktion Φ eines Druckverhältnisses π zwischen einem stromabwärtsseitigen Druck und einem stromaufwärtsseitigen Druck der Düse, welche in einer Gleichung des Satzes von Bernoulli enthalten ist, und eine lineare Funktion, welche die Funktion Φ annähert, veranschaulicht;
• 5 eine Verteilung von Verifikationsdaten zum Verifizieren einer Abschätzgenauigkeit des stromaufwärtsseitigen Turbinendrucks durch Gleichung 4 veranschaulicht;
• 6 einen Übereinstimmungsgrad eines abgeschätzten Werts des stromaufwärtsseitigen Turbinendrucks und eines tatsächlichen Werts des stromaufwärtsseitigen Turbinendrucks durch Gleichung 4 veranschaulicht;
• 7 ein Blockdiagramm ist, welches die Konfiguration zum Berechnen des stromaufwärtsseitigen Turbinendrucks, welche in der Steuerungsvorrichtung der Ausführungsform der vorliegenden Erfindung enthalten ist, veranschaulicht;
• 8 ein Beispiel der Anwendungen des abgeschätzten Werts des stromaufwärtsseitigen Turbinendrucks veranschaulicht; und
• 9 ein Beispiel der Anwendungen des abgeschätzten Werts des stromaufwärtsseitigen Turbinendrucks veranschaulicht.

Features, advantages and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying figures, in which the same reference symbols denote the same elements, and where:

• 1 Fig. 11 illustrates the schematic configuration of an internal combustion engine to which a control device of an embodiment of the present invention is applied;
• 2 Fig. 10 illustrates the relationship between the degree of closure of a variable nozzle, a turbine flow rate and an effective turbine opening area;
• 3 Fig. 11 illustrates the relationship among the opening of an EGR valve, an EGR valve flow rate and an effective EGR valve opening area;
• 4th illustrates a function Φ of a pressure ratio π between a downstream side pressure and an upstream side pressure of the nozzle contained in an equation of Bernoulli's Theorem and a linear function approximating the function Φ;
• 5 Fig. 4 illustrates a distribution of verification data for verifying an estimation accuracy of the upstream side turbine pressure by Equation 4;
• 6th a degree of correspondence of an estimated value of the upstream-side turbine pressure and an actual value of the upstream-side turbine pressure is illustrated by Equation 4;
• 7th Fig. 13 is a block diagram illustrating the configuration for calculating the turbine upstream pressure included in the control device of the embodiment of the present invention;
• 8th Figure 11 illustrates an example of the applications of the estimated value of the turbine upstream pressure; and
• 9 Fig. 11 illustrates an example of the applications of the estimated value of the turbine upstream pressure.

DETAILED DESCRIPTION OF EMBODIMENTS

Configuration of the internal combustion engine

1 illustrates the schematic configuration of an internal combustion engine 2 to which a control device of an embodiment of the present invention is applied. The internal combustion engine 2 according to the present embodiment is a single turbo system with a single turbo charger 20th . The internal combustion engine 2 contains an engine body 4th which is configured as a diesel engine. The engine body 4th is with a large number of (four in the drawing) cylinders 4a fitted and the cylinders 4a are each with a fuel injector 6th fitted.

The engine body 4th has one with an intake port 8th connected intake, which draws in fresh air from the outside. The intake duct 8th is using an air purifier 12 , a compressor 20a of the turbocharger 20th , an intercooler 14th and an intake throttle valve 16 in this order from the upstream side to the downstream side. In one area of the intake duct 8th which with the engine body 4th connected is an intake manifold 8a to distribute air to each cylinder 4a educated. The engine body 4th has a drain outlet, which is connected to an outlet channel 10 is connected, which exhaust gas discharges to the outside. The outlet duct 10 is with a turbine 20b of the turbocharger 20th fitted. The turbine 20b contains a variable nozzle 22nd . In one area of the outlet channel 10 which with the engine body 4th connected is an exhaust manifold 10a for collecting exhaust gas which is from each cylinder 4a is drained, trained.

The internal combustion engine 2 includes an EGR system 30th which some exhaust gas from the exhaust port 10 to the intake duct 8th recirculated. The EGR system 30th includes an EGR passage 32 which is the upstream side of the turbine 20b in the outlet duct 10 and the downstream side of the intake throttle valve 16 in the intake duct 8th connects. The EGR duct 32 is with an EGR cooler 34 and an EGR valve 36 provided in this order from the upstream side to the downstream side in a flow direction of EGR gas. The EGR duct 32 has a bypass channel 38 which is provided to bypass the EGR cooler. At a junction where the bypass duct 38 into the EGR duct 32 is a bypass valve 40 provided to a flow channel of the EGR gas between the bypass channel 38 and the EGR cooler 34 to switch.

The control device 100 which the internal combustion engine 2 controls is an electronic control unit (ECU) with at least one CPU, at least one ROM and at least one RAM. The ROM stores various kinds of data including various kinds of programs and maps for controlling the internal combustion engine 2 . When the programs stored in the ROM are loaded into the RAM and executed in the CPU, various functions are incorporated into the control device 100 implemented. The control device 100 may be formed from a variety of ECUs.

The control device 100 receives various information about the operating states and operating conditions of the internal combustion engine 2 of different types of sensors installed on the internal combustion engine 2 are attached. For example there is one near the air cooler 12 arranged air flow sensor 50 Information on a fresh air amount Gadly, which is the flow rate of fresh air entering the intake passage 8th is sucked. One in the intake manifold 8a arranged pressure sensor 52 inputs information on an intake manifold pressure Pim, which is the pressure within the intake manifold 8a is. The intake manifold pressure Pim is also an intake passage pressure, which is the pressure within the space of the intake passage 8th is the one with the EGR passage 32 connected is. One in the intake manifold 8a arranged temperature sensor 54 inputs information on an intake manifold temperature Tim, which is the temperature inside the intake manifold 8a is. One in the exhaust manifold 10a arranged temperature sensor 56 inputs information on an upstream-side turbine temperature Tus, which is the outlet duct internal temperature at an inlet side of the turbine 20b is. One downstream from the turbine 20b in the outlet duct 10 arranged pressure sensor 58 inputs information on a downstream turbine pressure Pds, which is an exhaust port internal pressure on an exhaust side of the turbine 20b is. One in the EGR valve 36 provided opening sensor gives information about an opening θegr of the EGR valve 36 one while one in the variable nozzle 22nd provided closing degree sensor information on a closing degree θvn of the variable nozzle 22nd enters. The control device 100 determines control parameters of the internal combustion engine 2 based on these pieces of information.

Estimation of an upstream turbine pressure

The control device 100 has functions that include estimating an upstream turbine pressure Pus, which is the exhaust port internal pressure on the inlet side of the turbine 20b is to include. A calculation of the upstream turbine pressure is performed using Equation 4. The following is a description of how Equation 4 is derived, that is, a method for deriving Equation 4.

Flow property equation of a turbine

When a fluid flows through a nozzle for which the law of conservation of energy is applied, the relationship between the quantity of state of the fluid before flowing through the nozzle and the quantity of state of the fluid after flowing through the nozzle follows Bernoulli's theorem. Here, if it is assumed that the turbine 20b is a nozzle, equation 5 is satisfied. In Equation 5, Mtb is a turbine flow rate, which is the flow rate of a gas passing through the turbine 20b flows through, and µAtb is an effective opening area of the turbine 20b when the turbine 20b showing the variable nozzle 22nd is considered to be a nozzle. An element Φ in Equation 5 is a function defined by Equation 1. $$\mathrm{M.}tb=\mu \mathrm{A.}tb\mathrm{\ast }Pus\mathrm{\ast }\sqrt{\frac{2}{\mathrm{R.}\mathrm{\ast }Tus}}\mathrm{\ast \; \Phi }\left(\frac{Pds}{Pus}\right)$$

Because the turbine 20b Work on the compressor 20a gives off, becomes the law of energy conservation in the turbine 20b not erected so that Bernoulli's theorem does not apply to the turbine 20b can be applied can. However, if µAtb in Equation 5 is regarded as a coefficient representing a fluidity of gas by expansion, Equation 5 can be used as an equation representing the flow characteristics of the turbine 20b represents. If the turbine work gets bigger, the turbine loses it 20b The gas flowing through has more energy, which makes it harder for the gas to flow. Therefore, if µAtb is a coefficient representing the fluidity of gas, the turbine work is convertible to µAtb, which enables Equation 5 to determine the flow characteristics of the turbine 20b expresses. Since µAtb in equation 5 corresponds to an effective opening area when the entire turbine 20b with the variable nozzle 22nd is regarded as a nozzle (effective turbine opening area of the entire turbine with the variable nozzle), µAtb is referred to as an effective turbine opening area in this specification.

The parameters that determine the effective turbine opening area are the degree of closure of the variable nozzle 22nd which in the turbine 20b is included, and the turbine flow rate. The degree of closure of the variable nozzle 22nd is a parameter that represents how far the variable nozzle is 22nd is closed, with a fully open position of the variable nozzle 22nd serves as a reference. The degree of closure of the variable nozzle 22nd is 0% when the variable nozzle 22nd is in the fully open position, whereas the degree of closure is 100% when the variable nozzle 22nd is in a fully closed position. 2 illustrates the relationship between the degree of closure θvn of the variable nozzle 22nd , the turbine flow rate Mtb and the effective turbine opening area µAtb. 2 is an example of experimental results obtained with an experimental internal combustion engine. In the experiment, effective turbine opening area values which satisfied Equation 5 were obtained for each degree of closure of the variable nozzle 22nd calculated keeping the turbine flow rate and the degree of closure of the variable nozzle 22nd was varied from 0% to 100%. The arithmetic operation was repeatedly performed while the turbine flow rate was varied step by step from a low flow rate to a large flow rate. As a result, a characteristic diagram of the effective turbine opening area as in FIG 2 illustrated.

Flow property equation of an EGR system

Incidentally, Bernoulli's theorem is on the EGR valve 36 even applicable which in the EGR system 30th is included. However, if the state quantity at the inlet of the EGR passage 32 as the state quantity of the upstream side of the EGR valve 36 uses the law of conservation of energy as a requirement of Bernoulli's theorem due to the influence of EGR cooling 34 , which is in the middle of the EGR duct 32 placed, not erected. The reason is that the EGR cooler 34 Removes heat from the gas. However, if µAegr is defined as a coefficient representing the flowability of a gas as in the case of Equation 5, it becomes the flow characteristics of the turbine 20b Equation 6 represents between the quantity of state at the inlet of the EGR passage 3 and the quantity of state at the outlet of the EGR passage 32 Fulfills. In Equation 6, Megr is an EGR valve flow rate, which is the flow rate of the gas passing through the EGR valve 36 flows through. The element Φ in Equation 5 is a function defined by Equation 1. The element µAegr in equation 6 corresponds to the effective opening area when the entire EGR system 30th with the EGR valve 36 is regarded as a nozzle (EGR valve effective opening area of the entire exhaust gas recirculation system including the EGR valve). Accordingly, µAegr is referred to as the EGR valve effective opening area in this specification. $$\mathrm{M.}eGr=\mu \mathrm{A.}eGr\mathrm{\ast }Pus\mathrm{\ast }\sqrt{\frac{2}{\mathrm{R.}\mathrm{\ast }Tus}}\mathrm{\ast \; \Phi }\left(\frac{Pim}{Pus}\right)$$

The parameters that determine the effective EGR valve opening area are the opening of the EGR valve 36 and the EGR valve flow rate. 3 illustrates the relationship between the opening θegr of the EGR valve 36 , the EGR valve flow rate Megr and the effective EGR valve opening area µAegr. 3 is an example of experimental results obtained with the experimental internal combustion engine. In the experiment, values of the effective EGR valve opening area which satisfied Equation 6 were obtained for each opening of the EGR valve 36 calculated keeping the EGR valve flow rate and the opening of the EGR valve 36 was varied from 0% to 100%. The arithmetic operation was repeatedly performed while the EGR valve flow rate was varied step by step from a low flow rate to a large flow rate. As a result, a characteristic diagram of the EGR valve effective opening area became as in FIG 3 illustrated.

The properties that are in 3 Illustrated are characteristics of the effective EGR valve opening area when the bypass valve 40 closed is. When the bypass valve 40 is open, the EGR cooler takes 34 no heat away from the gas. Accordingly, even when the EGR valve opening and the EGR valve flow rate are the same, the value of the effective EGR valve opening area which satisfies Equation 6 is different from the value when the bypass valve 40 closed is. For the effective EGR valve opening area was when the bypass valve 40 is open, another experiment was carried out and a property diagram that differs from that in 3 differs, was received.

Simplification of the function Φ

The function Φ contained in Equations 5 and 6 is a complicated function in which the pressure ratio π between the downstream side pressure and the upstream side pressure of the nozzle is used as a variable as shown in Equation 1. However, the function Φ can be simplified by dividing the function into a plurality of segments of the pressure ratio π by the piecewise linear method and linearly approximating the function for each segment of the pressure ratio π by a linear function. 4th illustrates the relationship between the function Φ and the pressure π as a variable of the function Φ. A curve shown with a broken line represents the relationship between the function Φ expressed by Equation 1 and the pressure π, whereas a polygonal line shown with a solid line represents the relationship between the function Φ, which was linearly approximated by the piecewise linear method, and represents the pressure π. In the example which is in 4th illustrated, the pressure ratio π is divided into six segments and linearly approximated for each segment.

The function Φ contained in Equation 5 can be simplified by the piecewise linear method as in the case of Equation 2. Using the simplified function Φ, the flow characteristics of the turbine 20b can be expressed by equation 7. The values of the coefficients a, b in equation 7 are defined for each segment of the pressure ratio. The values of the coefficients a, b corresponding to the segment which is defined based on the value of a ratio between the downstream side turbine pressure Pds and the upstream side turbine pressure Pus are substituted into Equation 7. However, the downstream side turbine pressure Pds is a current value, whereas the upstream side turbine pressure Pus is a previous value calculated at the previous calculation time. $$\mathrm{M.}tb=\mu \mathrm{A.}tb\mathrm{\ast }Pus\mathrm{\ast }\sqrt{\frac{2}{\mathrm{R.}\mathrm{\ast }Tus}}\mathrm{\ast }\left\{a\mathrm{\ast }\left(\frac{Pds}{Pus}\right)+b\right\}$$

The function Φ contained in Equation 6 can be simplified by the piecewise linear method as in the case of Equation 3. Using the simplified function Φ, the flow characteristics of the EGR system 30th can be expressed by equation 8. The values of the coefficients c, d in Equation 8 are defined for each segment of the pressure ratio. The values of the coefficients c, d corresponding to the segment defined based on the value of a ratio between the intake manifold pressure Pim and the upstream turbine pressure Pus are substituted into Equation 8. However, the intake manifold pressure Pim is a current value, whereas the upstream turbine pressure Pus is a previous value calculated at the previous calculation time. $$\mathrm{M.}eGr=\mu \mathrm{A.}eGr\mathrm{\ast }Pus\mathrm{\ast }\sqrt{\frac{2}{\mathrm{R.}\mathrm{\ast }Tus}}\mathrm{\ast }\left\{c\mathrm{\ast }\left(\frac{Pim}{Pus}\right)+d\right\}$$

Integration of the flow property equations

In equation 7, Tus can with the temperature sensor 56 can be measured and the Pds can with the pressure sensor 58 be measured. The element Mtb may Gadly based on the fresh air amount obtained with the air flow sensor 50 is measured, and the fuel flow rate Gf of the fuel entering the cylinder from the fuel injection valves 6th injected, can be calculated. The element µAtb is set based on the degree of closure θvn of the variable nozzle 22nd and the turbine flow rate Mtb is determined. Therefore, an equation which calculates Pus based on Tus, Pds, Mtb and µAtb can be obtained, by solving equation 7 for Pus. That is, to easily estimate the upstream turbine pressure, Equation 7 can be used.

However, noise tends to affect the readings from the airflow sensor 50 to be overlaid. Since the turbine flow rate Mtb depends on the fresh air amount obtained with the air flow sensor 50 is measured, is calculated, the noise included in the fresh air amount is directly superimposed on the calculation value of the turbine flow rate. Therefore, the estimated value of the upstream-side turbine pressure calculated by Equation 7 becomes due to the noise of the air flow sensor 50 influenced. Therefore, it cannot necessarily be said that the estimated value of the turbine upstream pressure is highly accurate.

Accordingly, the relationship shown in Equation 9 shown below is observed. The sum of the turbine flow rate Mtb and the EGR valve flow rate Megr coincides with a total flow rate of the exhaust gas flowing from the engine body 4th into the exhaust duct 10 is drained. The total flow rate is expressed as a sum of the amount of gas Gcyl within the cylinder and the fuel flow rate Gf. The amount of gas within the cylinder is determined with an equation of state based on the intake manifold pressure Pim obtained with the pressure sensor 52 is measured, and the intake manifold temperature Tim, which is obtained with the temperature sensor 54 is measured, predictable. The fuel flow rate is of a command value given to the fuel injector 6th from the control device 100 is given, predictable. $$\mathrm{M.}tb+\mathrm{M.}eGr=\mathrm{C.}cyl+Gf$$

In contrast to the air flow sensor 50 become the pressure sensor 52 and the temperature sensor 54 less likely to be affected by noise. Therefore, the total flow rate of the exhaust gas can be calculated with higher accuracy on the right side than on the left side of Equation 9. Equation 10, shown below, is obtained by substituting the right side of Equation 7 in Mtb on the left side of Equation 9 and substituting the right side of Equation 8 in Megr on the left side of Equation 9. Equation 4 is obtained by solving Equation 10 for Pus. $$\begin{array}{l}\mu \mathrm{A.}tb\mathrm{\ast }Pus\mathrm{\ast }\sqrt{\frac{2}{\mathrm{R.}\mathrm{\ast }Tus}}\mathrm{\ast }\left\{a\mathrm{\ast }\left(\frac{Pds}{Pus}\right)+b\right\}+\mu \mathrm{A.}eGr\mathrm{\ast }Pus\mathrm{\ast }\sqrt{\frac{2}{\mathrm{R.}\mathrm{\ast }Tus}}\mathrm{\ast }\left\{c\mathrm{\ast }\left(\frac{Pim}{Pus}\right)+d\right\}\\ =Gcyl+Gf\end{array}$$

In order to verify the estimation accuracy of the upstream turbine pressure by Equation 4, verification data with respect to various fuel injection amounts and various engine speeds as in FIG 5 illustrated. The verification data is formed from estimated values of the upstream turbine pressure and actual values of the upstream turbine pressure by Equation 4. 6th Fig. 13 is a graph view obtained by plotting the verification data on a plane having the estimated values (estimated pus) of the upstream side turbine pressure along a vertical axis and the actual values (actual pus) of the upstream side turbine pressure along a horizontal axis. As illustrated in the graph view, the estimated values and the actual values of the upstream turbine pressure by Equation 4 largely agree. This indicates that the upstream turbine pressure can be calculated with sufficient accuracy by using Equation 4.

The influence of the airflow sensor noise 50 is also applied to the calculation results of µAtb and µAegr in Equation 4. This is because µAtb is calculated based on the turbine flow rate Mtb and µAegr is calculated based on the EGR valve flow rate Megr. However, according to the relationship between µAtb and Mtb, which is shown in 2 is illustrated, the sensitivity of µAtb to the variation in Mtb is not very high. Similarly, according to the relationship between µAegr and Megr, which is shown in 3 is illustrated, the sensitivity of µAegr to the variation in Megr is also not very high. Therefore, it can be said that the noise of the air flow sensor 50 has a limited influence on the calculation results of µAtb and µAegr. Accordingly, the calculation accuracy of the upstream turbine pressure, which includes µAtb and µAegr as parameters, is sufficiently ensured.

Configuration and operation of the control device

7th Fig. 13 is a block diagram showing the configuration for calculating the turbine upstream pressure used in the control device 100 is included. When the CPU executes an upstream-side turbine pressure estimation program stored in the ROM, the control device operates 100 as arithmetic units 102 , 104 , 106 , 108 , 110 , what a 7th are illustrated.

When the upstream turbine pressure estimation program is executed, the control device detects 100 the parameters including a current value Pds of the downstream turbine pressure, a current value Pim of the intake manifold pressure, a current value Tus of the upstream turbine temperature, a current value θegr of the opening of the EGR valve 36 , a current value θvn of the degree of closure of the variable nozzle 22nd and a current value Gadly of the fresh air amount, each from respective sensors in a certain control period.

When the upstream turbine pressure estimation program is executed, the control device calculates 100 a current value Gcyl of the amount of gas within the cylinder, a current value Gf of the fuel flow rate, a current value Mtb of the turbine flow rate and a current value Megr of the EGR valve flow rate, each in a certain control period. The current value Mtb of the turbine flow rate is calculated as the sum total of the current value Gadly of the fresh air amount and the current value Gf of the fuel flow rate. The current value Megr of the EGR valve flow rate is calculated based on a difference between the sum total of the current value Gcyl of the amount of gas within the cylinder and the current value Gf of the fuel flow rate and the current value Mtb of the turbine flow rate.

The control device also stores 100 temporarily a previous value Pus_0 of the upstream-side turbine pressure, which is determined by an arithmetic unit described later 110 is calculated in the RAM in a certain control period.

The ROM of the control device 100 stores a first coefficient map which links each of the coefficients a, b of the linear function shown in equation 2 with the segments of the pressure ratio π. When a ratio between the current value Pds of the downstream side turbine pressure and the previous value Pus_0 of the upstream side turbine pressure is used as the pressure ratio π, the arithmetic unit is 102 configured to read out each of the coefficients a, b corresponding to the segment which is relevant for the pressure ratio π from the first coefficient map.

The ROM of the control device 100 stores a second coefficient map which links each of the coefficients c, d of the linear function shown in equation 3 with the segments of the pressure ratio π. When a ratio between the current value Pim of the intake manifold pressure and the previous value Pus_0 of the upstream side turbine pressure is used as the pressure ratio π, the arithmetic unit is 104 configured to read out each of the coefficients c, d corresponding to the segment which is relevant for the pressure ratio π from the second coefficient map.

The ROM of the control device 100 stores a map of an effective turbine opening area showing the relationship between the degree of closure of the variable nozzle 22nd , the turbine flow rate and the effective turbine opening area in the form of a map. The arithmetic unit 106 is configured to read out an effective turbine opening area µAtb from the effective turbine opening area map corresponding to the current value Mtb of the turbine flow rate and the current value θvn of the degree of closure of the variable nozzle 22nd .

The ROM of the control device 100 stores a map of an effective turbine opening area showing the ratio between the opening of the EGR valve 36 , the EGR valve flow rate and the effective EGR valve opening area, as in 3 is illustrated, maps in the form of a map. The arithmetic unit 108 is configured, from the map of the effective EGR valve opening area, an effective EGR valve opening area µAegr corresponding to the current value Megr of the EGR valve flow rate and the current value θegr of the opening of the EGR valve 36 read out.

The arithmetic unit 110 is configured to calculate a current value (estimated value) Pus of the upstream-side turbine pressure by Equation 4 based on the current value Pds of the downstream-side turbine pressure, the current value Pim of the intake manifold pressure, the current value Tus of the upstream-side turbine temperature, the sum total of the current value Gcyl of the gas amount within the cylinder and the current value Gf of the fuel flow rate, the effective turbine opening area µAtb, the effective EGR valve opening area µAegr and each of the coefficients a, b, c, d.

Using the estimated value of the upstream turbine pressure

The estimated value of the upstream turbine pressure calculated by Equation 4 is used variously. Among the uses of the estimated value of the turbine upstream pressure, typical uses are shown below.

A first use of the estimated value of the turbine upstream pressure is to estimate an EGR rate. The control device 100 contains an EGR rate estimation model which is described in 8th is illustrated. The EGR rate estimation model is configured to calculate the estimated value of the EGR rate based on the upstream side turbine pressure Pus, the fuel injection amount Q, the intake manifold pressure Pim, the fresh air amount Gadly, an engine water temperature Tw, and an intake air temperature Tair. The estimated value of the EGR rate is made by the control device 100 as one of the control parameters for the internal combustion engine 2 used.

A second use of the estimated value of the upstream turbine pressure is to suppress torque levels that are generated when the combustion mode is switched. When the catalyst is not active, the combustion mode can be switched from a normal combustion mode to a rich combustion mode in order to increase the exhaust gas temperature such that the catalyst is activated. In the rich combustion mode, the intake throttle valve is opened 16 throttled to decrease the amount of air and thereby achieve a rich air-fuel ratio. However, when the normal combustion mode is switched to the rich combustion mode, the intake throttle valve becomes 16 throttled, resulting in a pumping loss of the internal combustion engine 2 elevated. Calculated accordingly as in 9 illustrates the control device 100 the pumping loss based on the upstream side turbine pressure Pus and the intake manifold pressure Pim, and calculates an injection correction amount in accordance with the amount of pumping loss. The injection correction amount is added to the injection amount calculated based on a request torque to suppress the torque levels associated with the increase in pumping loss.

A third use of the estimated value of the turbine upstream pressure is to detect the risk of backflow of the EGR gas. When the intake manifold pressure is higher than the upstream turbine pressure, the EGR gas may be allowed into the EGR passage 32 flow back. The control device 100 compares the estimated value of the upstream turbine pressure with the reading of the intake manifold pressure to determine the risk of EGR gas backflow. Even if the internal combustion engine 2 is operated in an operating range in which the EGR valve 36 is open, the control device stops 100 the EGR valve 36 closed until the risk of EGR gas backflow disappears.

A fourth use of the estimated value of the upstream turbine pressure is to detect the risk of hardware failure in the internal combustion engine 2 . The control device 100 monitors the estimated value of the upstream turbine pressure, and performs boost pressure control and EGR rate control so that the upstream turbine pressure remains within a certain safety standard value.

Claims (1)

Control device for an internal combustion engine, the internal combustion engine comprising a turbocharger (20) and an exhaust gas recirculation system (30), the turbocharger comprising a turbine (20b) with a variable nozzle (22), the exhaust gas recirculation system (30) having an EGR duct (32), which connects a portion of an exhaust passage upstream of the turbine to an intake passage, and the EGR passage (32) has an EGR valve (36), the control device comprising: Means for detecting a current value (Pds) of a downstream turbine pressure, which is an exhaust port internal pressure at an exhaust side of the turbine; Means for detecting a current value (Pim) of an intake passage pressure, which is a pressure within a space of the intake passage connected to the EGR passage; Means for detecting a current value (Tus) of an upstream-side turbine temperature, which is an exhaust passage inside temperature at an inlet side of the turbine; Means for detecting a current value (θegr) of an opening of the EGR valve; Means for detecting a current value (θvn) of a degree of closure of the variable nozzle; Means for detecting a current value (Gadly) of an amount of fresh air, which is a flow rate of fresh air brought into the intake passage; Means for calculating a current value (Gcyl) of an amount of gas within a cylinder based on a pressure and a temperature of gas supplied to the cylinder; Means for calculating a current value (Gf) of a fuel flow rate of a fuel injection valve; Means for calculating a current value (Mtb) of a turbine flow rate, which is a flow rate of the gas flowing through the turbine, based on the current value (Gadly) of the fresh air amount and the current value (Gf) of the fuel flow rate; Means for calculating a current value (Megr) of an EGR valve flow rate based on a difference between a total of the current value (Gcyl) of the amount of gas within the cylinder and the current value (Gf) of the fuel flow rate and the current value (Mtb) of the Turbine flow rate; Means for storing a previous value (Pus_0) of the upstream turbine pressure, which is the exhaust port internal pressure on the inlet side of the turbine; Means for pre-storing a map of an effective turbine opening area which associates an effective turbine opening area of the entire turbine including the variable nozzle with the turbine flow rate and the degree of closure of the variable nozzle; Means for reading out an effective turbine opening area (µAtb) corresponding to the current value (Mtb) of the turbine flow rate and the current value (θvn) of the degree of closure of the variable nozzle from the map of the effective turbine opening area; Means for pre-storing a map of an effective EGR valve opening area which associates an effective EGR valve opening area of the entire exhaust gas recirculation system including the EGR valve with the EGR valve flow rate and the opening of the EGR valve; Means for reading out an effective EGR valve opening area (µAegr) corresponding to the current value (Megr) of the EGR valve flow rate and the current value (θegr) of the opening of the EGR valve from the map of the effective EGR valve opening area; Means for pre-storing a first coefficient map when a function (Φ) of a pressure ratio (π) between a downstream side pressure and an upstream side pressure of the nozzle, which is defined by equation 1, into a plurality of segments of the pressure ratio (π) by a piecewise linear Method is divided and for each segment of the pressure ratio (π) is linearly approximated by a linear function which is defined by equation 2, the first coefficient map coefficients (a, b) of the linear function which for each of the segments of the pressure ratio ( π) is defined, associated with the segments of the pressure ratio (π), where $$\mathrm{\Phi }\left(\pi \right)=\sqrt{\frac{\kappa }{\kappa -1}\mathrm{\ast }\left({\pi }^{\frac{2}{\kappa }}-{\pi }^{\frac{\kappa +1}{\kappa }}\right)}$$

is and equation 2 $$\mathrm{\Phi }\left(\pi \right)=a\mathrm{\ast }\pi +b$$

is; Means for reading out each of the coefficients (a, b) corresponding to the segment which is relevant for the pressure ratio (π) from the first coefficient map when a ratio between the current value (Pds) of the downstream turbine pressure and the previous value (Pus_0 ) the upstream turbine pressure is used as the pressure ratio (π) in equation 2; Means for pre-storing a second coefficient map which coefficients (c, d) of the linear function, which is defined for each of the segments of the pressure ratio (π), associated with the segments of the pressure ratio (π), if the function (Φ) of the pressure ratio (π) between the downstream side pressure and the upstream side pressure of the nozzle, which is defined by Equation 1, is divided into a plurality of segments of the pressure ratio (π) by a piecewise linear method, and for each segment of the pressure ratio (π) by a linear one Function defined by equation 3 is linearly approximated, where $$\mathrm{\Phi }\left(\pi \right)=c\mathrm{\ast }\pi +d$$

is; Means for reading out each of the coefficients (c, d) corresponding to the segment which is relevant for the pressure ratio (π) from the second coefficient map if a ratio between the current value (Pim) of the intake duct pressure and the previous value (Pus_0) des upstream turbine pressure is used as the pressure ratio (π) in Equation 3; Means for calculating the current value (Pus) of the upstream turbine pressure by Equation 4 based on the current value (Pds) of the downstream turbine pressure, the current value (Pim) of the intake manifold pressure, the current value (Tus) of the upstream turbine temperature, a total of the current value (Gcyl) of the amount of gas within the cylinder and the current value (Gf) of the fuel flow rate, the effective turbine opening area (µAtb), the effective EGR valve opening area (µAegr) and each of the coefficients (a, b, c, d) , in which $$Pus=\frac{\left(Gcyl+Gf\right)\mathrm{\ast }\sqrt{\frac{\mathrm{R.}\mathrm{\ast }Tus}{2}}-\mu \mathrm{A.}eGr\mathrm{\ast }Pim\mathrm{\ast }c-\mu \mathrm{A.}tb\mathrm{\ast }Pds\mathrm{\ast }a}{\mu \mathrm{A.}eGr\mathrm{\ast }d+\mu \mathrm{A.}tb\mathrm{\ast }b}$$

is; and means for controlling the internal combustion engine based on the current value (Pus) of the turbine upstream pressure.

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