JP5228972B2 - Control device for variable nozzle turbocharger - Google Patents

Description

  The present invention relates to a control device for a variable-nozzle variable turbocharger having a variable nozzle.

  2. Description of the Related Art As a turbocharger that is driven by engine exhaust energy and supercharges intake air, a variable displacement type equipped with a variable nozzle is known. In Patent Document 1, a nozzle position sensor (lift sensor) for detecting the actual nozzle opening is provided in order to prevent a decrease in drivability due to a deviation between the actual nozzle opening and the target nozzle opening. Describes a technique for feedback-controlling the actual nozzle opening detected by the above to the target nozzle opening.

JP 2005-240673 A

  However, such a nozzle position sensor for detecting the actual nozzle opening is expensive, and it is desirable to accurately obtain the actual nozzle opening without using such a sensor.

  Accordingly, the present invention has been made in view of the above-described problems, and a turbocharger that supercharges air taken in by an engine through an intake passage, and an inlet side opening of an exhaust turbine of the turbocharger. And is applied to a system having a variable nozzle for adjusting the capacity of the turbocharger and an actuator for driving the variable nozzle according to a command value. The command value is calculated based on the target nozzle opening, and is corrected based on the deviation between the target nozzle opening and the actual nozzle opening. The actual nozzle opening is calculated based on the turbine upstream pressure and the turbine downstream pressure.

  According to the present invention, the actual nozzle opening of the variable nozzle can be accurately obtained with an inexpensive configuration that does not require a nozzle position sensor that detects the actual nozzle opening of the variable nozzle. By using and correcting the command value, it is possible to suppress a decrease in drivability due to the deviation of the actual nozzle opening from the target nozzle opening.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the whole structure of the diesel engine provided with the control apparatus of the variable nozzle turbocharger which concerns on one Example of this invention. The flowchart which shows the flow of control of the variable nozzle which concerns on the said Example. Explanatory drawing which shows the catching phenomenon of the said variable nozzle.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an overall configuration of a diesel engine 1 to which an embodiment of the present invention is applied. The EGR passage 4 connecting the exhaust passage 2 and the collector portion 3a of the intake passage 3 is provided with a diaphragm EGR valve 6 that responds to a control pressure from a pressure control valve (not shown). The EGR valve 6 is controlled by the control unit 5 via the pressure control valve, and obtains a predetermined EGR rate according to the operating conditions. For example, the EGR rate becomes maximum in the low speed and low load region, and the EGR rate decreases as the rotational speed and load increase. In the vicinity of the intake port of the intake passage 3, an electrically controlled throttle valve 9 for adjusting the intake air amount (fresh air amount) is provided, and the opening degree of the throttle valve 9 is controlled by the control unit 5.

  The diesel engine 1 includes a common rail fuel injection device 10. In the common rail type fuel injection device 10, the fuel pressurized by the supply pump 11 is temporarily stored in the pressure accumulating chamber (common rail) 13 through the high pressure fuel supply passage 12, and then, from the pressure accumulating chamber 13 to each cylinder. The fuel is distributed to the fuel injection nozzles 14 and injected according to the opening and closing of the fuel injection nozzles 14. The fuel pressure in the pressure accumulating chamber 13 is variably adjusted by a pressure regulator (not shown), and the pressure accumulating chamber 13 is provided with a fuel pressure sensor 15 for detecting the fuel pressure. .

  The diesel engine 1 further includes a variable nozzle turbocharger 21 that is provided with an exhaust turbine 22 and a compressor 23 on the same axis. The exhaust turbine 22 is located downstream of the EGR passage 4 branch point of the exhaust passage 2 and a variable nozzle 24 for adjusting the capacity of the turbocharger is provided at the inlet side opening of the exhaust turbine 22, that is, the scroll inlet. It has a variable capacity configuration. That is, when the opening of the variable nozzle 24 is small, the characteristics of the small capacity are suitable for conditions with a small exhaust flow rate such as a low speed region, and when the opening of the variable nozzle 24 is large, the characteristic is as in the high speed region. Large capacity characteristics suitable for conditions with a large exhaust flow rate. The variable nozzle 24 is driven by a diaphragm actuator 25 that responds to a control pressure (control negative pressure), and the control pressure is generated through a pressure control valve 26 that is duty-controlled.

  In the exhaust passage 2 on the downstream side of the exhaust turbine 22, as a catalyst for purifying the exhaust gas, in order from the upstream side, an oxidation catalyst 27, a NOx purification catalyst 28 that adsorbs, desorbs and purifies NOx in the exhaust, and exhaust gas A particulate trapping filter or DPF 29 is provided as an exhaust aftertreatment device that traps exhaust particulate (PM) therein and periodically removes or regenerates the deposited PM by a method such as combustion.

  An air flow meter 31 for detecting the amount of intake air, that is, the amount of fresh air is disposed upstream of the compressor 23 interposed in the intake passage 3, and an air cleaner 32 is positioned further upstream. An intercooler 33 is provided between the compressor 23 and the collector unit 3a to cool the supercharged hot air.

  The control unit 5 that controls the pressure control valve 26 and the like includes a supercharging pressure sensor 41 that detects a supercharging pressure, a water temperature sensor 42 that detects a cooling water temperature, an accelerator, in addition to the detection signal of the air flow meter 31 described above. An accelerator opening sensor 43 that detects the amount of pedal depression, an intake air temperature sensor 44 that detects the intake air temperature, a rotational speed sensor 45 that detects the engine speed, and a turbine upstream pressure Ptin on the upstream side of the exhaust turbine 22 in the exhaust passage 2. A turbine upstream pressure sensor 46 to detect, a first oxygen sensor 47 to detect the oxygen concentration upstream of the oxidation catalyst 27 in the exhaust passage 2, and a first oxygen sensor to detect the oxygen temperature between the NOx purification catalyst 28 and the DPF 29 in the exhaust passage 2. 2 Oxygen sensor 48, inlet temperature sensor 49 for detecting the inlet temperature of the DPF 29, outlet temperature sensor 49 for detecting the outlet temperature of the DPF 29 Detection signals of the sensors such as DPF differential pressure sensor 51 for detecting the differential pressure across the temperature sensor 50, DPF 29 is input.

  Next, FIG. 2 is a flowchart showing a flow of control of the variable nozzle 24 of the turbocharger 21 that is stored and executed by the control unit 5.

  In step S11, the turbine upstream pressure Ptin on the upstream side of the exhaust turbine 22 in the exhaust passage 2, the turbine downstream pressure Ptout on the downstream side of the exhaust turbine 22 in the exhaust passage 2, and the like are read. The turbine upstream pressure Ptin is directly detected by the turbine upstream pressure sensor 46 described above. The turbine downstream pressure Ptout may be detected directly by providing a pressure sensor downstream of the turbine, or the pressure upstream of the DPF 29 may be calculated using the detected value of the DPF differential pressure sensor 51 as a reference. Further, as will be described later, it may be calculated based on the detection signal of the air flow meter 31.

  In step S12, a differential pressure ΔP = Ptin−Pttout before and after the exhaust turbine 22 is calculated based on the turbine upstream pressure Ptin and the turbine downstream pressure Ptout.

In step S13, an actual nozzle opening degree rAvnt which is an actual opening degree of the variable nozzle 24 is calculated by the following equation (3) ′.
rAvnt = Cep × (Ptout / (Ptin−Ptout)) ^1/2 (3) ′
Here, “Cep” is a pressure loss coefficient (fixed value) of the exhaust system. Therefore, the actual nozzle opening degree rAvnt is substantially obtained only by the turbine upstream pressure Ptin and the turbine downstream pressure Ptout, in other words, by the turbine upstream pressure Ptin and the differential pressure Ptin−Ptout before and after the turbine.

  In step S14, a target nozzle opening tAvnt that is a target value of the nozzle opening of the variable nozzle 24 is calculated. The target nozzle opening tAvnt is obtained on the basis of the engine rotation speed, the fuel injection amount corresponding to the load, etc. in consideration of fuel consumption, efficiency, parts protection, etc. More specifically, the engine rotation speed and the fuel injection amount The target fresh air amount and the target EGR rate are obtained from the above, and the target exhaust gas flow rate is obtained from the target fresh air amount and the fuel injection amount. Based on the target exhaust gas flow rate, the target EGR rate, the actual supercharging pressure, etc. The nozzle opening tAvnt is obtained.

  In step S15, it is determined whether a deviation ΔAvnt between the actual nozzle opening rAvnt and the target nozzle opening tAvnt is less than a predetermined determination value Δs. This determination value is set to 0 or a small value close to 0, and may be simply a fixed value, or may be changed according to the engine operating state, for example, during acceleration or deceleration.

  If the deviation ΔAvnt is less than the determination value Δs, the process proceeds to step S16, and a dither correction value described later is set to zero. That is, the command value sAvnt is not corrected. Next, in step S19, a command value dAvnt to the actuator 25 that drives the variable nozzle 24 is calculated based on the target nozzle opening tAvnt. A specific method for calculating the command value dAvnt will be described later.

  On the other hand, if the deviation ΔAvnt is greater than or equal to the determination value Δs, a dither correction value, which is a correction value for correcting the command value dAvnt, is calculated in step S17. Specifically, the period or amplitude of a dither signal (vibration signal) described later is increased by the dither correction value.

  In step S18, an operation situation in which the deviation ΔAvnt is equal to or greater than the determination value Δs, that is, an operation situation that causes a so-called catching phenomenon in which the target nozzle opening and the actual nozzle opening are transiently deviated as will be described later. The target nozzle opening tAvnt, the turbine upstream pressure Ptin, and the deviation ΔAvnt at this time are stored and stored in a predetermined storage area provided in the control unit 5, that is, a learning storage area, and set for calculation of the command value dAvnt after the next time. Reflect (learning means). That is, when an operation situation that causes a catching phenomenon occurs, the cycle or amplitude of the dither signal is increased by the dither correction value.

  In step S19, a command value dAvnt to the actuator 25 that drives the variable nozzle 24 is calculated. That is, the basic command value dAvnt is calculated using the target nozzle opening tAvnt, and the command value dAvnt (dither signal) is corrected using the dither correction value as described above.

  The calculation of the command value dAvnt will be described. In the variable nozzle 24, which is driven and controlled by the actuator 25 using a negative pressure as a drive source, there is hysteresis that the characteristics differ depending on the operation direction. It is well known. In other words, when the variable nozzle is moved in the direction in which the nozzle opening increases (that is, when the variable nozzle is opened), it must be moved against the exhaust reaction force acting on the nozzle. When the variable nozzle is moved from the position where the nozzle opening is large to the direction where the nozzle opening is reduced, the variable nozzle can be moved to the target nozzle opening. Therefore, the actual nozzle opening is smaller than the target nozzle opening. Thus, the command value necessary to obtain the same target nozzle opening when moving the variable nozzle in the direction in which the nozzle opening increases, and conversely when moving the variable nozzle in the direction in which the nozzle opening decreases. The phenomenon in which the two differ is the hysteresis in this actuator. In general, hysteresis is also referred to as a history phenomenon, and is a phenomenon that is determined by the history of the state in which a thing has passed in the past, without being determined only by the conditions under which the state is currently placed.

  As a method for eliminating the hysteresis in the actuator of such a variable nozzle, there is a dither control technique as disclosed in Japanese Patent Laid-Open No. 2001-132463 as the third embodiment. Briefly, a basic command value is obtained from the target nozzle opening tAvnt, and a vibration signal having a predetermined amplitude and a predetermined cycle is superimposed on the basic command value, so that a predetermined value is always reflected while reflecting a change in the basic command value. A signal that oscillates with an amplitude and a period is generated, and this is used as a command value dAvnt to drive the actuator 25. Actually, this command value dAvnt is given in the form of an ON duty ratio of a pulse signal for driving the pressure control valve 26 that generates the control pressure (negative pressure), and a pressure signal corresponding to this, that is, the control pressure, is given. It will be output to the actuator.

  Next, characteristic configurations and operational effects of the present invention will be described with reference to the above-described embodiment.

  [1] As shown in FIG. 1, a turbocharger 21 that supercharges air taken in by the engine 1 via the intake passage 3 and an opening on the inlet side of the exhaust turbine 22 of the turbocharger 21 are provided. And a variable nozzle 24 for adjusting the capacity of the turbocharger 21 and an actuator 25 for driving the variable nozzle 24 according to the command value sAvnt. Further, as shown in FIG. 2, target nozzle opening setting means (S14) for setting the target nozzle opening tAvnt of the variable nozzle 24 based on the engine operating state and the like, and the actual nozzle opening rAvnt of the variable nozzle 24 are detected. Actual nozzle opening degree detecting means (S13), command value calculating means (S19) for calculating the command value sAvnt based on the target nozzle opening degree tAvnt, the target nozzle opening degree tAvnt and the actual nozzle opening degree rAvnt Command value correcting means (S15 to S17) for correcting the command value sAvnt based on the deviation ΔAvnt. And it has a turbine upstream pressure detection means such as a turbine upstream pressure sensor 46 for detecting the turbine upstream pressure Ptin, and a turbine downstream pressure acquisition means for acquiring the turbine downstream pressure Ptout. The actual nozzle opening degree rAvnt is calculated based on the turbine upstream pressure Ptin and the turbine downstream pressure Ptout.

  With such a configuration, the actual nozzle opening degree rAvnt is satisfactorily calculated based on the turbine upstream pressure Ptin and the turbine downstream pressure Ptout without using an expensive sensor for detecting the actual nozzle opening degree rAvnt of the variable nozzle 24. By correcting the command value sAvnt based on the actual nozzle opening rAvnt, the deviation between the actual nozzle opening rAvnt and the target nozzle opening tAvnt is suppressed, and the accuracy of the nozzle opening control is improved. be able to.

The reason why the actual nozzle opening degree rAvnt can be satisfactorily calculated based on the turbine upstream pressure Ptin and the turbine downstream pressure Ptout will be described using the following formula using Bernoulli's theorem.
And exhaust pipes of pipe friction loss ΔP = λ × (l / d ) × ρ × (U 2/2)
P: pressure λ: Euler number l: tube length d: tube inner diameter ρ: density U: flow velocity and Bernoulli's equation Qexh = ρ × A × U
= Ρ × A × (2 × ΔP / ρ) ^1/2
= A × (2 × ρ × ΔP) ^1/2
Qexh: displacement (exhaust mass flow rate)
A: Area

· Applying the turbine downstream pressure equation of the Bernoulli Ptout = λ × (l / d ) × ρ × (U 2/2)
Uep = (2 × Ptout / (λ / (l / d) / ρ)) ^1/2
Qexh = ρ × Aep × Uep
= Aep / (λ / (l / d)) ^1/2 × (2 × ρ × Ptout) ^1/2
= Cep × (2 × ρ × Ptout) ^1/2 (1)
Cep: Pressure loss coefficient determined by the exhaust system Ptout: Turbine downstream pressure Uep: Exhaust flow velocity, turbine upstream pressure, and downstream pressure are applied to the Bernoulli equation Qexh = Avnt × (2 × ρ × (Ptin−Ptout)) ^1/2 . (2)
Avnt: Variable nozzle opening area Ptin: Turbine upstream pressure

By transforming Bernoulli's equation, equation (2) for obtaining the variable nozzle opening area Avnt is obtained. In this equation, the exhaust flow rate and the density ρ are required to calculate the variable nozzle opening area Avnt. Usually, in order to obtain the exhaust flow rate, it is common to calculate based on the detected value of the air flow meter. However, since the air flow meter is mounted immediately after the air cleaner, the distance to the exhaust turbine 22 is long and the response is delayed. Becomes larger. For this reason, when trying to obtain the variable nozzle opening area Avnt during the transition, the accuracy is low. Further, since the density ρ changes due to the influence of temperature and pressure, this also becomes an error factor.

In view of this, the present inventor examined the application of equation (1) to equation (2) in order to eliminate such errors.
・ From formulas (1) and (2) Avnt = Cep × (Ptout / (Ptin−Ptout)) ^1/2 (3)
As apparent from the equation (3), since Cep is a fixed value determined by the exhaust system, the actual nozzle opening degree rAvnt can be calculated and estimated satisfactorily only by the turbine downstream pressure Ptout and the turbine upstream pressure Ptin. be able to. In other words, the actual nozzle opening degree rAvnt can be calculated and estimated satisfactorily by the turbine downstream pressure Ptout (or the turbine upstream pressure Ptin) and the differential pressure before and after the turbine (Ptin−Ptout).

  [2] In the case where the exhaust aftertreatment device 29 is provided on the downstream side of the exhaust turbine 22 as in the above embodiment, the actual nozzle opening degree rAvnt is corrected according to the blockage ratio of the exhaust aftertreatment device 29. As a result, the actual nozzle opening rAvnt can be obtained appropriately in a form commensurate with the blockage ratio of the exhaust aftertreatment device 29.

  [3] More specifically, the exhaust aftertreatment device is the DPF 29, and the blockage rate is the PM deposition amount of the DPF 29. As a result, the actual nozzle opening rAvnt can be obtained appropriately according to the amount of PM deposited on the DPF 29.

  [4] When the variable nozzle 24 is driven and controlled by the actuator 25 using fluid pressure (negative pressure), the command value dAvnt is set using a dither control technique. That is, the command value calculation means superimposes a conversion means for converting the target nozzle opening tAvnt into a basic command value and a vibration signal (dither signal) having a predetermined amplitude and a predetermined period on the basic command value. Signal superimposing means for generating the command value sAvnt. Thus, by obtaining the command value sAvnt using the dither control technique, the hysteresis in the actuator 25 of the variable nozzle 24 can be reduced and eliminated as described above.

  [5] Referring to FIG. 3, when the nozzle opening is opened against the exhaust pressure, due to mechanical factors of the variable nozzle 24, high exhaust pressure, that is, the turbine upstream pressure Ptin, etc. 3, the nozzle opening cannot be moved toward the target nozzle opening tAvnt, and the deviation (deviation) ΔAvnt between the actual nozzle opening rAvnt and the target nozzle opening tAvnt increases. There is a risk of getting caught.

  In order to suppress / avoid the occurrence of such a catching phenomenon, the period or amplitude of the vibration signal as the dither signal is corrected based on the deviation ΔAvnt between the actual nozzle opening rAvnt and the target nozzle opening tAvnt. More specifically, when the deviation ΔAvnt is greater than or equal to a predetermined determination value Δs, the period or amplitude of the vibration signal is increased. In this way, by increasing the period or amplitude of the dither signal, the occurrence of the above-mentioned catching phenomenon can be effectively suppressed.

  [6] More preferably, as an operating situation in which the deviation ΔAvnt is equal to or greater than the determination value Δs, that is, an operating situation in the vicinity of the time T1 at which the catching phenomenon occurs, for example, the turbine upstream pressure Ptin and the target nozzle opening tAvnt at that time And the deviation ΔAvnt are stored and stored in the learning storage area (S18), and are reflected in the calculation of the command value sAvnt from the next time on (learning means). . That is, when the driving situation stored in the learning storage area is reached, the occurrence of a catching phenomenon can be suppressed and prevented by correcting the dither signal as described above.

[7] The turbine downstream pressure may be calculated by the following equation (1) ′ using an intake air detection unit that detects an intake air amount (intake mass flow rate) Qint as the turbine downstream pressure acquisition unit.
Ptout = ((Qint + Qf) / Cep) ² / 2ρ (1) ′
Ptout: Turbine downstream pressure Qint: Intake amount (intake mass flow rate)
Qf: Fuel injection amount Cep: Pressure loss coefficient of exhaust system ρ: Exhaust density The above equation (1) ′ is obtained from equation (1) using Bernoulli's theorem described above and equation (4) below.
Qexh = Qint + Qf (4)
Qexh: displacement (exhaust mass flow rate)
In this way, a sensor that directly detects the turbine downstream pressure by using the intake air detection means that detects the intake air amount (intake mass flow rate) Qint such as the air flow meter 31 that is generally used in existing engines. With a simple configuration that is not used, the turbine downstream pressure Ptout can be estimated well and the actual nozzle opening rAvnt can be obtained.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, in the above embodiment, the turbine downstream pressure Ptout is estimated using the detection signal of the air flow meter 31, but a turbine downstream pressure sensor that directly detects the downstream pressure of the exhaust turbine 22 may be provided. Further, since the detection accuracy of the turbine upstream pressure Ptin is low in the low load region and the operation region where the exhaust pressure (turbine upstream pressure Ptin) is low, the correction control as described above may be prohibited in such a region. good. Furthermore, an electric actuator such as an electric motor may be used as the actuator of the variable nozzle 24. In such a case, the driving force of the actuator may be increased instead of increasing the cycle or amplitude of the dither signal as correction of the command value sAvnt. In addition, the above correction control may be performed only when the exhaust pressure rises to cause the above-described catching phenomenon, that is, when the nozzle opening is closed.

DESCRIPTION OF SYMBOLS 1 ... Diesel engine 2 ... Exhaust passage 5 ... Control unit 21 ... Turbocharger 24 ... Variable nozzle 25 ... Actuator 26 ... Pressure control valve 46 ... Turbine upstream pressure sensor

Claims (8)

A turbocharger that supercharges air taken in by an engine through an intake passage, and is provided at an inlet side opening of an exhaust turbine of the turbocharger, and is variable to adjust the capacity of the turbocharger This is applied to a variable nozzle turbocharger having a nozzle and an actuator for driving the variable nozzle according to the command value. Based on the target nozzle opening and the actual nozzle opening, the command value calculating means opens the target nozzle. In the control device for the variable nozzle turbocharger provided with the command value correcting means for correcting the command value set based on the degree,
Turbine upstream pressure detection means for detecting turbine upstream pressure;
Turbine downstream pressure acquisition means for acquiring the turbine downstream pressure,
The control apparatus for a variable nozzle turbocharger, wherein the actual nozzle opening is calculated based on the turbine upstream pressure and the turbine downstream pressure.   2. The control device for a variable nozzle turbocharger according to claim 1, wherein the actual nozzle opening is calculated based on a deviation between the turbine upstream pressure and the turbine downstream pressure and the turbine upstream pressure. . An exhaust aftertreatment device is provided downstream of the exhaust turbine,
3. The control device for a variable nozzle turbocharger according to claim 1, wherein the actual nozzle opening is corrected in accordance with a blocking ratio of the exhaust aftertreatment device. 4. The exhaust aftertreatment device is a DPF,
The control device for a variable nozzle turbocharger according to claim 3, wherein the blocking ratio is a PM accumulation amount of the DPF.   The command value calculation means is a signal for generating the command value by superimposing a conversion means for converting the target nozzle opening to a basic command value and a vibration signal having a predetermined amplitude and a predetermined period on the basic command value. The control device for a variable nozzle turbocharger according to any one of claims 1 to 4, further comprising a superposition unit.   The said command value correction | amendment means enlarges the period or amplitude of the said vibration signal, when the deviation of the said target nozzle opening and an actual nozzle opening is more than predetermined determination value. Variable nozzle turbocharger control device.   A learning means is provided for storing the driving situation at this time in a learning storage area when the deviation is equal to or greater than a predetermined determination value, and reflecting it in calculation of a command value by the command value calculation means. 6. A control device for a variable nozzle turbocharger according to 6. Intake detection means for detecting the intake air amount,
Ptout = ((Qint + Qf) / Cep) ² / 2ρ (1) ′
Ptout: Turbine downstream pressure Qint: Intake air amount Qf: Fuel injection amount Cep: Pressure loss coefficient of exhaust system ρ: Exhaust density The turbine downstream pressure acquisition means calculates the turbine downstream pressure by the above equation (1) ′. The control device for a variable nozzle turbocharger according to any one of claims 1 to 7.

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