JP6513440B2 - Controller of variable displacement turbocharger - Google Patents

Description

  The present invention relates to a control device of a variable displacement turbocharger.

  2. Description of the Related Art Conventionally, Exhaust Gas Recirculation (EGR) is known in which part of exhaust gas is recirculated from the exhaust side to the intake side of an engine in order to reduce NOx and improve fuel consumption. In order to perform EGR, it is required that the pressure on the exhaust side be maintained higher than the pressure on the intake side. Therefore, for example, in Patent Document 1, the opening degree of the variable nozzle allows EGR even in a high load state in which the pressure on the intake side tends to be higher than the pressure on the exhaust side in an engine equipped with a variable displacement turbocharger. Is disclosed.

JP 2002-332879 A

  By the way, when the torque request amount from the driver falls sharply, the fuel injection amount also falls sharply. At this time, the exhaust pressure decreases with the decrease of the fuel injection amount, while the high rotation state of the turbocharger is maintained by inertia, so that the pressure on the intake side is maintained at a high state. Therefore, the differential pressure between the pressure on the intake side and the pressure on the exhaust side decreases, and there is a possibility that the target amount of EGR gas can not be introduced even if the EGR valve is controlled to the fully open state.

  An object of the present invention is to provide a control device of a variable displacement turbocharger capable of securing a differential pressure necessary for introducing EGR gas between an intake side and an exhaust side.

A controller of a variable displacement turbocharger that solves the above problems includes a unit flow rate calculation unit that calculates a unit flow rate of EGR gas in the EGR valve by dividing a target EGR amount by the maximum opening area of the EGR valve; The boost coefficient, which is the pressure of the working gas in which the gas and the intake air are mixed, and the second-order coefficient from the second-order coefficient data that defines the second-order coefficient for each EGR temperature, which is the temperature of the EGR gas flowing into the EGR valve And a primary coefficient selection unit for selecting the primary coefficient from primary coefficient data that defines the primary coefficient for each EGR temperature, the unit flow rate x, the secondary coefficient a, and the primary factor b, when the minimum differential pressure between y required by the EGR valve, the minimum pressure difference calculating unit for calculating the minimum differential pressure in accordance with an arithmetic expression y = ax 2 + ^bx, before A target pressure setting unit that sets a target pressure of exhaust gas flowing into the turbocharger so that the minimum differential pressure is generated by the EGR valve, and a control that controls the opening degree of the variable nozzle of the turbocharger according to the target pressure And a unit.

In the above configuration, simulation results obtained by setting the boost pressure, the EGR temperature, the maximum opening area, and the EGR pressure that is the pressure of the EGR gas flowing into the EGR valve to the theoretical formula of the compressible fluid are obtained. The polynomial approximation of the equation y = ax ² + bx, and the quadratic coefficient and the primary coefficient of the equation obtained from the simulation result are used. According to the above configuration, the target pressure is set such that the EGR gas having the target EGR amount flows even if the EGR valve has the maximum opening area. Thereby, it is possible to secure the differential pressure necessary for introducing the EGR gas between the pressure on the intake side and the pressure on the exhaust side.

In the control device of the variable displacement turbocharger, the secondary coefficient has a larger value as the boost pressure is lower if the EGR temperature is the same.
In the above simulation, the EGR pressure is a value obtained by adding the minimum differential pressure to the boost pressure. Therefore, the density of the EGR gas flowing into the EGR valve decreases as the boost pressure decreases. According to the above configuration, as the density of the EGR gas is smaller, a second-order coefficient having a larger value is selected. In this way, it is possible to select a secondary coefficient that has a large impact on the minimum differential pressure according to the density of the EGR gas.

In the control device of the variable displacement turbocharger, the secondary coefficient has a larger value as the EGR temperature is higher if the boost pressure is the same.
EGR gas density becomes smaller as the EGR temperature is higher. According to the above configuration, as the density of the EGR gas is smaller, a second-order coefficient having a larger value is selected. In this way, it is possible to select a secondary coefficient that has a large impact on the minimum differential pressure according to the density of the EGR gas.

In the controller of the variable displacement turbocharger, the lower the EGR temperature, the smaller the primary coefficient. Therefore, the primary coefficient is selected according to the density of the EGR gas.
The control device of the variable displacement turbocharger includes a basic expansion ratio selection unit that selects the basic expansion ratio from basic expansion ratio data that defines a basic expansion ratio for each engine speed and fuel injection amount, and exhaust at the outlet of the turbine An outlet pressure calculator for calculating an outlet pressure which is a gas pressure, a basic target pressure calculator for calculating a basic target pressure by multiplying the basic expansion ratio by the outlet pressure, and the EGR gas flowing into the EGR valve A pressure loss calculation unit for calculating the pressure loss of the pressure drop, and a required target pressure calculation unit for calculating the required target pressure by adding the boost pressure, the minimum differential pressure, and the pressure loss; Preferably, the setting unit sets the maximum value of the basic target pressure and the required target pressure as the target pressure.

  According to the above configuration, when the basic target pressure is lower than the required target pressure, the required target pressure is set to the target pressure, whereby the differential pressure necessary for introducing the EGR gas is secured. On the other hand, when the required target pressure is lower than the basic target pressure, the basic target pressure is set to the target pressure, so that the differential pressure necessary for introducing the EGR gas is ensured and the expansion ratio suitable for the operating state of the engine It can drive a turbocharger.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows schematic structure of the engine system by which one Embodiment of the control apparatus of a variable displacement turbocharger is mounted. FIG. 2 is a block diagram showing an example of a configuration of a control device of a variable displacement turbocharger. FIG. 5 is an operation block diagram showing a part of the operation performed by the operation unit. The graph which shows an example of basic expansion ratio data typically. The graph which shows an example of the result of simulation. The graph which shows an example of secondary coefficient data typically. The graph which shows an example of primary coefficient data typically. The top view which shows the structure of a modification typically.

  An embodiment embodying a control device for a variable displacement turbocharger will be described with reference to FIGS. 1 to 7. First, an overall configuration of an engine system in which a variable displacement turbocharger is mounted will be described with reference to FIG.

  As shown in FIG. 1, the engine system includes a diesel engine 10 (hereinafter referred to as the engine 10). The cylinder block 11 of the engine 10 is formed with four cylinders 12 arranged in a line. Fuel is injected from the injectors 13 into the respective cylinders 12. The cylinder block 11 is connected to an intake manifold 14 for supplying intake air to each cylinder 12 and an exhaust manifold 15 into which exhaust gas from each cylinder 12 flows.

  In the intake passage 16 connected to the intake manifold 14, an air cleaner (not shown), a compressor 18 constituting a turbocharger 17, and an intercooler 19 are provided in this order from the upstream side. The exhaust passage 20 connected to the exhaust manifold 15 is provided with a turbine 22 connected to the compressor 18 via a connecting shaft 21 and constituting a turbocharger 17.

  The engine system includes an EGR passage 25 connecting the exhaust manifold 15 and the intake passage 16. An EGR cooler 26 is provided in the EGR passage 25, and an EGR valve 27 capable of changing the flow passage cross-sectional area of the EGR passage 25 is provided on the side of the intake passage 16 in the EGR cooler 26. When the EGR valve 27 is in the open state, a part of the exhaust gas is introduced into the intake passage 16 as the EGR gas through the EGR passage 25, and the working gas which is a mixture of the exhaust gas and the intake air is Is supplied.

  The turbocharger 17 is a variable displacement turbocharger (VNT: Variable Nozzle Turbo) in which a variable nozzle 28 is disposed in the turbine 22. The variable nozzle 28 has an opening degree changed by driving an actuator 29 provided with a stepping motor, so that the pressure of the exhaust gas in the exhaust manifold 15 is an exhaust pressure Pem that is a pressure of the exhaust gas flowing into the turbine 22. And, the inflow Gti of the exhaust gas to the turbine 22 is adjusted. The opening degree of the variable nozzle 28 is controlled by a VNT controller 50 which is a controller of a variable displacement turbocharger.

  The engine system comprises various sensors. The intake air amount sensor 31 is located upstream of the compressor 18 in the intake passage 16 and detects an intake air amount Ga which is a mass flow rate of the intake air flowing into the compressor 18. The EGR pressure sensor 33 and the EGR temperature sensor 34 are located between the EGR cooler 26 and the EGR valve 27 in the EGR passage 25. The EGR pressure sensor 33 detects an EGR pressure Pr, which is the pressure of the EGR gas flowing into the EGR valve 27, and the EGR temperature sensor 34 detects an EGR temperature Tr, which is the temperature of the EGR gas flowing into the EGR valve 27. The boost pressure sensor 36 is located between the connecting portion of the EGR passage 25 to the intake passage 16 and the intake manifold 14 and detects a boost pressure Pb which is the pressure of the working gas. The working gas temperature sensor 37 is attached to the intake manifold 14 and detects a working gas temperature Twg which is the temperature of the working gas flowing into the cylinder 12. The engine speed sensor 38 detects an engine speed Ne that is the speed of the crankshaft 30. The variable nozzle opening degree sensor 40 detects a nozzle opening degree VTa which is the opening degree of the variable nozzle 28 based on the drive amount of the actuator 29. Each of the above sensors outputs a signal indicating the detected value detected to the VNT controller 50.

  As shown in FIG. 2, the VNT controller 50 (hereinafter simply referred to as the controller 50) includes a controller 51 including a CPU, a ROM, a RAM, and the like. The control unit 51 includes an acquisition unit 52 that acquires an external signal, an operation unit 53 that performs various calculations, and a storage unit 54 that stores various data such as various control programs and basic expansion ratio data 71. The control device 50 also includes a nozzle drive unit 55 that drives the actuator 29. The control unit 51 calculates the target pressure tPem of the exhaust pressure Pem using the signal acquired by the acquisition unit 52 and the various data stored in the storage unit 54 in accordance with the various control programs stored in the storage unit 54. The opening degree of the variable nozzle 28 is controlled so that the target pressure tPem is realized. A signal indicating the atmospheric pressure Patm from the atmospheric pressure sensor 41 and a signal indicating the fuel injection amount Gf from the fuel injection control unit 42 that controls the fuel injection are input to the control device 50. Further, a signal indicating the target EGR amount tGr is input to the control device 50 from the EGR control unit 43 that controls the opening degree of the EGR valve 27. The target EGR amount tGr is an EGR amount that embodies an excess air ratio that can suppress the generation of black smoke, the generation of NOx, and the like based on the operating state of the engine 10.

  Based on the signals output from the above-mentioned various sensors, the acquisition unit 52 calculates the intake air amount Ga, the EGR pressure Pr, the EGR temperature Tr, the boost pressure Pb, the working gas temperature Twg, the engine rotational speed Ne, the nozzle opening degree VTa, Get the atmospheric pressure Patm. Further, the acquisition unit 52 acquires the fuel injection amount Gf based on the signal from the fuel injection control unit 42, and acquires the target EGR amount tGr based on the signal from the EGR control unit 43.

  The computing unit 53 has an inflow temperature Tti which is a temperature of exhaust gas flowing into the turbine 22, an inflow amount Gti which is a mass flow rate of exhaust gas flowing into the turbine 22, and an outlet pressure Pte which is a pressure of exhaust gas at the outlet of the turbine 22. And a second calculation unit 53b for calculating a target pressure tPem of the exhaust pressure Pem. The calculation unit 53 further includes a third calculation unit 53 c that calculates the target opening area tA of the variable nozzle 28 using the inflow temperature Tti, the inflow amount Gti, the outlet pressure Pte, and the target pressure tPem. The target pressure tPem is a very important parameter for driving the turbocharger 17. The target pressure tPem has an optimum value that varies in accordance with the purpose, such as reduction of NOx and PM, suppression of over rotation or surging of the turbocharger 17, formation of a minimum differential pressure in the EGR valve 27 when performing EGR, etc. It is.

  The third operation unit 53c calculates a target opening area tA by substituting each value into Expression (1) based on Bernoulli's theorem. The third calculation unit 53c substitutes the inflow temperature Tti for “T1”, the inflow amount Gti for “G”, the outlet pressure Pte for “P2”, and the target pressure tPem for “P1”, which is the calculation result “ The target aperture area tA is calculated as “A”. In equation (1), κ is the specific heat ratio of the exhaust gas, and R is the gas constant.

  The calculation unit 53 calculates the target nozzle opening degree tVT that embodies the target opening area tA obtained from the equation (1), and changes the opening degree of the variable nozzle 28 from the nozzle opening degree VTa to the target nozzle opening degree tVT. Calculate the commanded opening degree VTc, which is the opening degree required for. The arithmetic unit 53 outputs the instruction opening degree VTc to the nozzle drive unit 55.

  The nozzle drive unit 55 generates a drive signal for changing the opening degree of the variable nozzle 28 by an amount corresponding to the instruction opening degree VTc input from the calculation unit 53, and outputs the generated drive signal to the actuator 29.

  As shown in FIG. 3, the first computing unit 53 a includes various computing units. The working gas amount calculation unit 56 calculates a working gas amount Gwg which is a mass flow rate of the working gas supplied to the cylinder 12. The working gas amount calculation unit 56 performs predetermined calculations based on the state equation P × V = Gwg × R × T as the boost pressure Pb, the engine speed Ne, the displacement D of the engine 10, the working gas temperature Twg, and the gas constant R The working gas amount Gwg is calculated by using this method.

The EGR amount calculation unit 57 calculates an EGR amount Gr which is a mass flow rate of the EGR gas by subtracting the intake air amount Ga from the working gas amount Gwg.
The EGR rate calculating unit 58 calculates an EGR rate η (= Gr / Gwg) by dividing the EGR amount Gr by the working gas amount Gwg.

  The inflow temperature calculation unit 59 calculates the inflow temperature based on the working gas amount Gwg, the EGR rate η, the fuel injection amount Gf which is an input value from the fuel injection control unit 42, and the inflow temperature data 60 stored in the storage unit 54. Calculate Tti. The inflow temperature data 60 is data in which the temperature of the exhaust gas is uniquely defined using the working gas amount Gwg, the EGR rate η, and the fuel injection amount Gf as parameters based on experiments performed beforehand. Then, the inflow temperature calculation unit 59 selects the inflow temperature Tti corresponding to the working gas amount Gwg, the EGR rate η, and the fuel injection amount Gf from the inflow temperature data 60.

  The inflow amount calculation unit 61 calculates an inflow amount Gti which is a mass flow rate of the exhaust gas flowing into the turbine 22. The inflow amount calculation unit 61 calculates the inflow amount Gti by adding the fuel injection amount Gf to the intake air amount Ga.

  The EGR pressure loss calculation unit 62 calculates the pressure loss ΔPr of the EGR gas in the EGR passage 25 based on the EGR amount Gr and the EGR passage data 63 stored in the storage unit 54. The EGR passage data 63 is data in which the pressure loss ΔPr of the EGR gas between the inlet of the EGR passage 25 and the EGR pressure sensor 33 is defined for each of the EGR amounts Gr based on a previously performed experiment or the like. The EGR pressure loss calculation unit 62 selects a pressure loss ΔPr corresponding to the EGR amount Gr from the EGR passage data 63.

The exhaust pressure calculation unit 64 calculates the exhaust pressure Pem by adding the pressure loss ΔPr to the EGR pressure Pr.
The outlet pressure calculator 65 calculates an outlet pressure Pte based on the inflow temperature Tti, the inflow amount Gti, the atmospheric pressure Patm, and the exhaust passage data 66 stored in the storage unit 54. The exhaust passage data 66 indicates that the pressure loss ΔPep generated in the exhaust gas from the exit of the turbine 22 to the atmosphere based on the experiment conducted in advance is the volumetric flow based on the inflow Gti to the turbine 22. 1/2) It is the data specified for each / Pem. The outlet pressure calculator 65 selects a pressure loss ΔPep corresponding to the inflow amount Gti from the exhaust passage data 66, and calculates the outlet pressure Pte by adding the selected pressure loss ΔPep to the atmospheric pressure Patm. Thus, the number of sensors exposed to high temperature exhaust gas can be reduced by calculating the outlet pressure Pte.

  The second arithmetic unit 53 b includes various arithmetic units. The basic expansion ratio selection unit 70 selects a basic expansion ratio πS that is an expansion ratio suitable for the operating state of the engine 10 from the basic expansion ratio data 71 stored in the storage unit 54. Then, the basic target pressure calculation unit 72 calculates the basic target pressure PemS by multiplying the outlet pressure Pte by the basic expansion ratio πS.

  As shown in FIG. 4, the basic expansion ratio data 71 is data in which a basic expansion ratio πS is uniquely defined with the engine speed Ne and the fuel injection amount Gf as parameters based on experiments performed beforehand. . Each of the basic expansion ratios πS has a specific engine speed Ne at which the fuel injection amount Gf is maximum in the middle speed range of the engine 10. In each of the basic expansion ratios πS, the corresponding fuel injection amount Gf decreases as the engine speed Ne decreases in a region where the engine speed Ne is lower than the specific engine speed Ne, and the specific engine speed In a region higher than Ne, the corresponding fuel injection amount Gf decreases as the engine speed Ne increases. Thus, surging of the turbocharger 17 is suppressed in the low rotation range of the engine 10, and over rotation of the turbocharger 17 is suppressed in the high rotation range of the engine 10.

  The secondary coefficient selection unit 73 selects a secondary coefficient a from the secondary coefficient data 74 stored in the storage unit 54. Further, the primary coefficient selection unit 75 selects the primary coefficient b from the primary coefficient data 76 stored in the storage unit 54.

  The secondary coefficient a and the primary coefficient b will be described with reference to FIGS. The inventor has defined the secondary coefficient a and the primary coefficient b based on the result of the simulation performed using the above equation (1). The inventor sets the maximum opening area Amax of the EGR valve 27 as a fixed value to “A” in the equation (1), and the EGR pressure Pr to “P1”, the boost pressure Pb to “P2”, and “T1”. The EGR temperature Tr was set as a fluctuation value. Then, various values are substituted into the EGR pressure Pr, the boost pressure Pb, and the EGR temperature Tr to obtain the EGR operation amount Grc, and the unit flow rate x (= Grc / Amax) in the EGR valve 27 and the pressure difference in the EGR valve 27 The relationship between An example of the result is shown in FIG.

In FIG. 5, the boost pressure Pb is indicated by an absolute pressure, and the simulation result in the case where the EGR pressure Pr is varied with the boost pressure Pb and the EGR temperature Tr fixed at predetermined values (determination coefficient R ² ≒ 1) is shown. Here, since “A” is set to the maximum opening area Amax of the EGR valve 27, the pressure difference at the EGR valve 27 is the pressure difference required to introduce the EGR gas for the amount of the EGR operation amount Grc. This is the minimum value (minimum differential pressure y). Based on the results of this simulation, the inventor of the present invention approximated the relationship between the minimum differential pressure y and the unit flow rate x with the polynomial of equation (2), and examined the secondary coefficient a and the primary coefficient b.
y = ax ² + bx ... (2)

  Then, the inventor can define the secondary coefficient a for each of the boost pressure Pb and the EGR temperature Tr, and the primary coefficient b has a constant value for each of the EGR temperatures Tr regardless of the boost pressure Pb. I found it to be.

  As shown in FIG. 6, the secondary coefficient data 74 is data in which a secondary coefficient a is defined for each of the boost pressure Pb and the EGR temperature Tr. Further, as shown in FIG. 7, the primary coefficient data 76 is data in which a primary coefficient b is defined for each EGR temperature Tr. The secondary coefficient selection unit 73 selects a secondary coefficient a corresponding to the boost pressure Pb and the EGR temperature Tr from the secondary coefficient data 74. Further, the primary coefficient selection unit 75 selects a primary coefficient b corresponding to the EGR temperature Tr from the primary coefficient data 76.

  The unit flow rate calculating unit 78 calculates the unit flow rate x in the EGR valve 27 by dividing the target EGR amount tGr from the EGR control unit 43 by the maximum opening area Amax of the EGR valve 27. The maximum opening area Amax is a value set according to the type of the EGR valve 27 when the control device 50 is set up.

  The minimum differential pressure calculation unit 79 calculates the secondary coefficient a selected by the secondary coefficient selection unit 73, the primary coefficient b selected by the primary coefficient selection unit 75, the unit flow rate x calculated by the unit flow rate calculation unit 78, and the above The minimum differential pressure y at the EGR valve 27 is calculated by substituting it into (2).

  The required target pressure calculation unit 80 calculates a required target pressure PemN that is a pressure necessary for the exhaust pressure Pem to introduce the EGR gas for the target EGR amount tGr. The required target pressure calculation unit 80 calculates the required target pressure PemN by adding the boost pressure Pb, the minimum differential pressure y, and the pressure loss ΔPr.

The target pressure setting unit 81 sets the maximum value of the basic target pressure PemS and the required target pressure PemN as the target pressure tPem.
The third operation unit 53c substitutes the inflow temperature Tti, the inflow amount Gti, the outlet pressure Pte, and the target pressure tPem thus calculated into the equation (1) to obtain the target opening area tA of the variable nozzle 28. Calculate

  Next, the operation of the control device 50 described above will be described. The controller 50 controls the opening degree of the variable nozzle 28 so that the exhaust pressure Pem becomes the target pressure tPem. The target pressure tPem is a value at which the pressure difference at the EGR valve 27 is set to the minimum differential pressure y or more based on the result of the simulation using the above equation (1). The minimum differential pressure y is the minimum value of the pressure difference necessary to introduce the EGR gas for the target EGR amount tGr when the EGR valve 27 is set to the maximum opening area Amax. Thereby, even if the EGR valve 27 is controlled to the maximum opening area Amax, it is necessary to introduce the EGR gas for the target EGR amount tGr into the intake passage 16 between the boost pressure Pb and the exhaust pressure Pem. Differential pressure can be secured.

According to the VNT control device 50 of the above embodiment, the following effects can be obtained.
(1) Since the target pressure tPem is set to a pressure that produces the minimum differential pressure y in the EGR valve 27, securing the differential pressure necessary for introducing the EGR gas between the boost pressure Pb and the exhaust pressure Pem Can.

(2) The pressure of the EGR gas flowing into the EGR valve 27 is a value obtained by adding the minimum differential pressure y to the boost pressure Pb. Therefore, the density of the EGR gas flowing into the EGR valve 27 decreases as the boost pressure Pb decreases. Also, the EGR gas has a lower density as the temperature is higher . In this regard, the secondary coefficient data 74 is defined larger secondary coefficient a higher boost pressure Pb is low if the EGR temperature Tr is the same is, as the EGR temperature Tr is higher if the boost pressure Pb is the same A large second-order coefficient a is specified. As a result, it is possible to select a secondary coefficient a having a large influence on the minimum differential pressure y according to the density of the EGR gas.

  (3) The secondary coefficient a is obtained by selecting from the secondary coefficient data 74 based on the boost pressure Pb and the EGR temperature Tr. As a result, it is possible to simplify the calculation when obtaining the secondary coefficient a.

(4) The primary coefficient b is obtained by selecting from the primary coefficient data 76 based on the EGR temperature Tr. As a result, it is possible to simplify the calculation when obtaining the primary coefficient b. Also, the primary coefficient b can be selected according to the density of the EGR gas.
(5) The minimum differential pressure y can also be determined, for example, by substituting the boost pressure Pb, the EGR temperature Tr, the target EGR amount tGr, the maximum opening area Amax, and the like with respect to equation (1). However, not only are the calculations complicated, but if calculations are required each time the variable nozzle 28 is controlled, the load on the control device 50 increases. In this respect, as described in the above (2) to (4), the load on the control device 50 can be reduced by obtaining the minimum differential pressure y by a simple calculation.

  (6) The controller 50 sets the maximum value of the basic target pressure PemS and the required target pressure PemN to the target pressure tPem. Thus, the exhaust pressure Pem corresponding to the operating state of the engine 10 is embodied while securing the exhaust pressure Pem required for introducing the EGR gas.

  (7) With regard to the minimum differential pressure y, the simulation results were approximated not by power approximation but by polynomial approximation. As a result, it is possible to cope with x = 0, that is, when controlling the EGR valve 27 in a fully closed state without performing special control. Thereby, the load on the control device 50 can be reduced.

In addition, the said embodiment can also be changed suitably as follows and can also be implemented.
The basic expansion ratio may be any expansion ratio suitable for the operating state of the engine 10, and is not limited to the one selected by the engine speed Ne and the fuel injection amount Gf, for example, the engine speed Ne and the fuel injection amount In addition to Gf, it may be selected based on the amount of change of the fuel injection amount Gf, the amount of change of the accelerator opening degree, and the like.

  The control device 50 may set the target pressure tPem to a value equal to or higher than the required target pressure PemN. Therefore, the control device 50 may continue to set the required target pressure PemN to the target pressure tPem, and in addition to the required target pressure PemN and the basic target pressure PemS, for example, calculates the target pressure for the engine 10 in a transient state. Alternatively, the target pressure tPem may be selected from among these.

  The fuel injection control unit that controls the fuel injection amount Gf and the VNT control device 50 may be incorporated in the same control device. Further, the EGR control unit 43 that controls the opening degree of the EGR valve 27 and the VNT control device 50 may be incorporated in the same control device. Further, the control device 50 may include a target EGR amount calculation unit that obtains the same calculation result as the target EGR amount tGr of the EGR control unit 43.

Next, technical ideas that can be grasped from the above embodiment and modifications will be additionally described below.
(Supplementary Note 1)
A pressure control device for controlling the pressure on the primary side based on a target amount of compressible fluid flowing through a connection connecting the primary side and the secondary side,
A unit flow rate calculation unit that calculates a unit flow rate of the compressible fluid at the connection portion by dividing the target amount by the flow passage cross-sectional area of the connection portion;
A secondary coefficient selection unit that selects the secondary coefficient from secondary coefficient data that defines a secondary coefficient for each of the pressure on the secondary side and the temperature of the compressible fluid flowing into the connection portion;
A primary coefficient selection unit that selects the primary coefficient from primary coefficient data that defines a primary coefficient for each temperature of the compressible fluid;
Assuming that the unit flow rate is x, the secondary coefficient is a, the primary coefficient is b, and the minimum differential pressure necessary at the connection is y, the minimum differential pressure is calculated according to the equation y = ax ² + bx Minimum differential pressure calculation unit,
And a target pressure setting unit configured to set a target pressure on the primary side by using an addition value of the pressure on the secondary side and the minimum differential pressure as a lower limit value.

As in the above embodiment, the pressure on the secondary side, the temperature of the compressible fluid flowing into the connection, the flow passage cross-sectional area of the connection, and the pressure on the primary side are set with respect to the equation (1) The above equation y = ax ² + bx can be obtained by approximating the simulation result of the obtained minimum differential pressure. Then, the secondary coefficient a and the primary coefficient b in the above equation are defined from the result of the simulation. According to the above configuration, the target pressure on the primary side is set so that the compressible fluid of the target amount flows through the connection. Thereby, the flow rate of the compressible fluid passing through the connection can be controlled.

  For example, as illustrated in FIG. 8, when the connection portion 88 is provided in the connection passage 87 that connects the supply target 85 and the pressure adjustment mechanism 86 such as a pump or a regulator, the pressure control device 90 includes the pressure adjustment mechanism 86. Controls the pressure P11 on the primary side with respect to the connection portion 88. The pressure control device 90 holds the secondary coefficient data and the primary coefficient data based on the result of the simulation described above in the storage unit 91, acquires the temperature T11 on the primary side from the temperature sensor 92, The pressure P22 on the next side is acquired. The pressure control device 90 then calculates the secondary coefficient a and the primary coefficient b based on the target flow rate of the compressible fluid supplied from the primary side to the secondary side, the temperature T11 on the primary side, and the pressure P22 on the secondary side. And calculate the target value of the pressure P11 on the primary side. The pressure control device 90 controls the pressure adjustment mechanism 86 so that the pressure P11 on the primary side becomes the target value.

  DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 15 ... Exhaust manifold, 16 ... Intake passage, 17 ... Turbocharger, 18 ... Compressor, 19 ... Intercooler, 20 ... Exhaust passage, 21 ... Coupling shaft, 22 ... Turbine, 25 ... EGR passage, 26 ... EGR passage Cooler, 27: EGR valve, 28: variable nozzle, 29: actuator, 31: intake air amount sensor, 33: EGR pressure sensor, 34: EGR temperature sensor, 36: boost pressure sensor, 37: working gas temperature sensor, 38 ... Engine rotational speed sensor, 40 ... variable nozzle opening sensor, 41 ... atmospheric pressure sensor, 42 ... fuel injection control unit, 43 ... EGR control unit, 50 ... VNT control device, 51 ... control unit, 52 ... acquisition unit, 53 ... Arithmetic unit, 53a: first arithmetic unit, 53b: second arithmetic unit, 53c, third operation , 54: storage unit, 55: nozzle drive unit, 56: working gas amount calculation unit, 57: EGR amount calculation unit, 58: EGR rate calculation unit, 59: inflow temperature calculation unit, 60: inflow temperature data, 61: inflow Amount operation unit 62: EGR pressure loss operation unit 63: EGR passage data 64: exhaust pressure operation unit 65: outlet pressure operation unit 66: exhaust passage data 70: basic expansion ratio selection unit 71: basic expansion Ratio data 72 Basic target pressure calculation unit 73 Secondary coefficient selection unit 74 Secondary coefficient data 75 Primary coefficient selection unit 76 Primary coefficient data 78 Unit flow rate calculation unit 79 Minimum difference Pressure operation unit, 80: necessary target pressure operation unit, 81: target pressure setting unit, 85: supply target, 86: pressure adjustment mechanism, 87: connection passage, 88: connection unit, 90: pressure control device, 91: storage unit , 92 ... temperature sensor, 93 Pressure sensor.

Claims (5)

A unit flow rate calculating unit that calculates a unit flow rate of EGR gas in the EGR valve by dividing the target EGR amount by the maximum opening area of the EGR valve;
The boost pressure, which is the pressure of the working gas in which the EGR gas and the intake air are mixed, and the secondary coefficient data that defines the secondary coefficient for each EGR temperature, which is the temperature of the EGR gas flowing into the EGR valve A secondary coefficient selection unit that selects the next coefficient;
A primary coefficient selection unit that selects the primary coefficient from primary coefficient data that defines a primary coefficient for each EGR temperature;
Assuming that the unit flow rate is x, the secondary coefficient is a, the primary coefficient is b, and the minimum differential pressure necessary for the EGR valve is y, the minimum differential pressure is calculated according to the equation y = ax ² + bx Minimum differential pressure calculation unit,
A target pressure setting unit configured to set a target pressure of exhaust gas flowing into a turbocharger so that the minimum differential pressure is generated by the EGR valve;
And a controller configured to control an opening degree of a variable nozzle of the turbocharger according to the target pressure. The control device of a variable displacement turbocharger according to claim 1, wherein the secondary coefficient has a larger value as the boost pressure is lower if the EGR temperature is the same. The control device of a variable displacement turbocharger according to claim 1 or 2, wherein the secondary coefficient has a larger value as the EGR temperature is higher if the boost pressure is the same. The control device of a variable displacement turbocharger according to any one of claims 1 to 3, wherein the first order coefficient has a larger value as the EGR temperature is lower. A basic expansion ratio selection unit that selects the basic expansion ratio from basic expansion ratio data that defines a basic expansion ratio for each engine speed and fuel injection amount;
An outlet pressure calculator for calculating an outlet pressure which is a pressure of exhaust gas at an outlet of the turbine;
A basic target pressure calculation unit that calculates a basic target pressure by multiplying the basic expansion ratio by the outlet pressure;
A pressure loss calculating unit that calculates a pressure loss of the EGR gas flowing into the EGR valve;
And a required target pressure calculation unit that calculates a required target pressure by adding the boost pressure, the minimum differential pressure, and the pressure loss.
The control device for a variable displacement turbocharger according to any one of claims 1 to 4, wherein the target pressure setting unit sets a maximum value of the basic target pressure and the required target pressure as the target pressure.

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