Controlling a target boost pressure for a turbocharger

Abstract

Method (200) for controlling a target boost pressure (210) for a turbocharger (110) driven by exhaust gas of an internal combustion engine (105), wherein the method (200) comprises the following steps: - Determining (205) a filling-based target boost pressure (205) based on a filling of the internal combustion engine (105); - Sampling (215) of an actual boost pressure (215); - Determine (235, 245, 247) a carried actual boost pressure (225) based on the actual boost pressure (215); - Determining (255) an offset (250) based on the fill-based target boost pressure (205); and - Control (220) of the target boost pressure (210) by means of a first-order timer (220) to the filling-based target boost pressure (205), - if the actual boost pressure (225) exceeds a value (265) that is smaller by the offset (250) than the target boost pressure (205) based on the filling.

Description

[0001] A motor vehicle comprises a powertrain with an internal combustion engine. The internal combustion engine is equipped with a turbocharger, which includes an exhaust turbine and a compressor. The exhaust turbine is driven by a stream of exhaust gas from the internal combustion engine and, in turn, drives the compressor, which compresses fresh air for the engine. The resulting pressure of the fresh air is called boost pressure. The boost pressure can be controlled, for example, by adjusting the variable turbine geometry of the turbocharger. Other methods of adjusting the boost pressure include venting excess compressed air on the compressor side or bypassing a portion of the exhaust gas flow around the exhaust turbine.

[0002] Particularly when the powertrain is used in a motor vehicle, rapid or frequent load changes of the combustion engine may be necessary. This involves changes to various parameters of the combustion engine, one of which is the boost pressure. For smooth power delivery, it is crucial that the actual boost pressure of the turbocharger follows a predetermined target boost pressure as quickly as possible and without overshoot. Until now, this has sometimes been achieved using complex proportional-integral differential controllers (PID controllers), whose parameters required extensive parameter adjustments.

[0003] DE 10 2011 006 227 A1 relates to a technique for feedforward control of a controller. In this technique, the target variable is changed abruptly in successive phases.

[0004] DE 197 51 977 A1 proposes to adjust the turbine geometry of a turbocharger depending on the sum of a predetermined value and a feedforward control value.

[0005] DE 10 2007 050 026 A1 concerns the determination of an error in the regulation of a value to a predetermined value.

[0006] DE 10 2008 042 510 A1 discloses a method and a device for torque build-up in a turbocharged internal combustion engine with a correction for a pressure offset that depends on the current air quantity, wherein the corrected pressure offset is low-pass filtered, which suggests a first-order timing element.

[0007] DE 10 2013 014 721 A1 describes a method for operating a motor vehicle with a turbocharger, which, in addition to a target control setpoint corresponding to the target boost pressure, also specifies a different initial control setpoint, which can be determined depending on the current boost pressure and is brought towards the target control setpoint.

[0008] The object of the present invention is to provide an improved technique for controlling a target boost pressure for a turbocharger. The invention achieves this object by means of the subject matter of the independent claims. Dependent claims describe preferred embodiments.

[0009] A turbocharger is driven by exhaust gas from an internal combustion engine. A method for controlling a target boost pressure of the turbocharger comprises the steps of determining a charge-based target boost pressure based on the charge of the internal combustion engine; sampling an actual boost pressure; determining a carried actual boost pressure based on the actual boost pressure; determining an offset based on the charge-based target boost pressure; and controlling the target boost pressure to the charge-based target boost pressure by means of a first-order timer if the carried actual boost pressure exceeds a value that is less than the charge-based target boost pressure by the offset.

[0010] In other words, the target boost pressure of a turbocharger's boost pressure control system is adjusted to prevent the actual boost pressure from exceeding the target boost pressure. This is achieved by temporarily reducing the target boost pressure when the actual boost pressure rises sharply, thus minimizing the difference between the two values. This temporary reduction of the target boost pressure is preferably accomplished using an offset.

[0011] The method can be used between a control unit that determines the target boost pressure based on the combustion engine's fuel load and a control or regulation system that maintains the boost pressure at the determined target boost pressure. Alternatively, either the former or the latter component can be adapted accordingly. In one embodiment, the determination of the target boost pressure based on fuel load, the described method, and the boost pressure control or regulation can also be performed in a single, combined process.

[0012] The offset determines the difference between the charge-based target boost pressure and the actual boost pressure that must be reached at a minimum to cause the described temporary reduction in the target boost pressure. It is preferred that the offset be determined based on the charge-based target boost pressure and an internal combustion engine speed. This allows for improved modulation of non-linear relationships between the internal combustion engine speed and the turbocharger boost pressure.

[0013] The offset can be determined, in particular, using a first characteristic map. This map is defined by the engine speed and the charge-based target boost pressure.

[0014] The actual boost pressure is preferably determined based on the sum of the actual boost pressure and a defined value, which is determined based on the charge-based target boost pressure and the actual boost pressure. The determined actual boost pressure can be easily ascertained and better reflects the actual conditions prevailing at the turbocharger.

[0015] The defined value can be determined, in particular, based on the gradients of the target boost pressure (based on the charge level) and the actual boost pressure. By considering these gradients, the change in the respective parameter over time is incorporated into the determination. The gradients can each be determined by differentiating the affected parameter with respect to time. Using these time-derived parameters allows for improved modulation of the turbocharger's dynamics.

[0016] It is particularly preferred that the defined value is determined using a second characteristic map. This second characteristic map spans between a gradient of the charge-based target boost pressure and the gradient of the actual boost pressure.

[0017] In a first embodiment, the time constant of the first-order timing element can be fixed, or in a further embodiment, it can be dynamically determined based on the charge-based target boost pressure and the actual boost pressure. This allows for improved control of how the target boost pressure approaches the charge-based target boost pressure over time. Ultimately, the actual boost pressure can be approached more quickly and without overshoot to the charge-based target boost pressure.

[0018] The time constant can be determined based on gradients of the charge-based target boost pressure and the actual boost pressure. The procedure can be the same as for determining the aforementioned value using the second characteristic map. In particular, the time constant can be determined using a third characteristic map. In one embodiment, the second and third characteristic maps are integrated and provide two parameters: the aforementioned value and the described time constant.

[0019] A device for controlling a target boost pressure for a turbocharger driven by the exhaust gas of an internal combustion engine comprises a first interface for determining a charge-based target boost pressure; a second interface for sensing an actual boost pressure; and a processing unit configured to determine a synchronized actual boost pressure based on the actual boost pressure; to determine an offset based on the charge-based target boost pressure; and to control the target boost pressure to the charge-based target boost pressure by means of a first-order timer if the synchronized actual boost pressure exceeds a value that is lower than the target boost pressure by the offset. In particular, the device can be configured to perform the procedure described above.The device can be used on an internal combustion engine with a turbocharger and integrated with a control device for the internal combustion engine or a control device for the turbocharger. The processing unit of the device can, in particular, comprise a programmable microcomputer or microcontroller.

[0020] The invention will now be described in more detail with reference to the attached figures, wherein Fig. 1. a powertrain for a motor vehicle; Fig. 2. A flowchart of a procedure for controlling a target boost pressure of a turbocharger of the powertrain of Fig. 1; Fig. 3. An illustration of the procedure of Fig. 2; and Fig. 4 Target and actual boost pressures at a turbocharger with conventional control; Fig. 5 Target and actual boost pressures at a turbocharger when controlled by the method of Fig. 2 represents.

[0021] Fig. Figure 1 shows a powertrain 100, specifically for a motor vehicle. The powertrain 100 comprises an internal combustion engine 105, a turbocharger 110, and optionally other elements such as a clutch, a transmission, or a drive wheel, which are integrated into Fig. Figure 1 is not shown. The turbocharger 110 comprises an exhaust gas turbine 115 and a compressor 120, which are typically coupled to each other by means of a rigid shaft. Air is compressed by the compressor 120 and supplied to the internal combustion engine 105. There, the air is mixed with fuel and the mixture is combusted. The resulting exhaust gas is fed to the exhaust gas turbine 115, which mechanically drives the compressor 120.

[0022] The boost pressure provided by the turbocharger 110 can be controlled. This control can be achieved, for example, by adjusting a variable turbine geometry or by adjusting a valve that influences the amount of exhaust gas flowing through the exhaust turbine 115. The target boost pressure to be set can be provided, for example, by an engine control unit 125. The engine control unit 125 can also be configured to receive parameters from the internal combustion engine 105, such as temperature, air mass, or lambda value in the exhaust system, and to control actuators on the internal combustion engine 105 that influence the operating state. These actuators can include, in particular, a fuel injector, valve timing, or ignition timing.

[0023] The actual boost pressure of the turbocharger 110 can be controlled or regulated to the specified target boost pressure by means of a device 130. The device 130 can be integrated with the engine control unit 125. It is proposed to manipulate the specified target boost pressure under certain circumstances in order to achieve an improved temporal profile of the actual boost pressure relative to the target boost pressure. In particular, the actual boost pressure should approach the target boost pressure as quickly as possible, not exceed it, and exhibit the smoothest possible profile. In the illustrated embodiment, the device 130 is integrated with the turbocharger control unit 110; however, in another embodiment, the device 130 can also be built separately from it.

[0024] The device 130 can be connected to the engine control unit 125, for example, via a first interface 135 to receive the target boost pressure. A second interface 140 can be provided to measure the actual boost pressure of the turbocharger 110. In one embodiment, the turbocharger 110 is controlled via a third interface 145. Optionally, a fourth interface 150 is also provided, through which the device 130 is connected to a speed sensor 155 or another component that provides the rotational speed 218 of the internal combustion engine 105.

[0025] Fig. Figure 2 shows a flowchart of a method 200 for controlling the target boost pressure of the turbocharger 110. The method 200 can be executed, in particular, on the device 130, for example, in the form of a computer program. The method 200 is configured to provide a target boost pressure 210 based on a charge-based target boost pressure 205, which can be received via interface 135. This target boost pressure 210 can be set, for example, by means of a proportional (P) controller, a pi (PI) controller, a PID (Pulse Interference Diagnosis) controller, or another conventional controller on the turbocharger 110. In another embodiment, the actual boost pressure 215 on the turbocharger 110 can also be set using the method 200. In some embodiments, the method 200 also makes use of a rotational speed 218, which it can receive, in particular, via interface 150.

[0026] It is proposed to adjust the fill-based target boost pressure 205 under certain circumstances by means of an offset 250 and subsequent first-order timer (PT1) 220 in order to prevent the actual boost pressure 215 from rising too rapidly and, in particular, from overshooting the fill-based target boost pressure 205. For this purpose, the supplied target boost pressure 210 is temporarily reduced so that it approaches the fill-based target boost pressure 205 at a predetermined rate.

[0027] Preferably, a current boost pressure 225 is determined, which can be calculated in an additive element 247 as the sum of the current boost pressure 215 and a value 230. The value 230 is determined based on the charge-based target boost pressure 205 and the current boost pressure 215. Preferably, in a step 235, a gradient of the charge-based target boost pressure 205 is determined, and in a step 240, a gradient of the current boost pressure 215 is determined. The desired value 230 can be determined based on the determined gradients, for example, using a characteristic map 245.

[0028] An offset 250 is preferably determined based on the engine speed 218 and the charge-based target boost pressure 205. A map 255 can be used for this purpose. The offset 250 is subtracted from the charge-based target boost pressure 205 in step 260. The result is compared with the actual boost pressure 225 in step 265. If the actual boost pressure 225 exceeds the result, i.e., if the actual boost pressure 225 is less than the offset 250 below the charge-based target boost pressure 205, the timer 220 is activated.

[0029] A time constant 270 of the timing element 220 can be fixed or dynamically determined. For dynamic determination, the time constant 270 can be determined based on the fill-based target boost pressure 205 and the actual boost pressure 215. For this purpose, the gradients determined in steps 235 and 240 can again be considered. It is preferred that the time constant 270 be determined using a characteristic map 275, and further preferably based on the gradients.

[0030] Fig. Figure 3 shows an illustration of the procedure 200 of Fig. 2. Time is specified in the horizontal direction and boost pressure in the vertical direction.

[0031] From time 305 onwards, the actual boost pressure 225 is less than the fill-based target boost pressure 205 by less than the offset 250. The target boost pressure 210 is temporarily reduced by means of the offset 250 in order to gradually approach the fill-based target boost pressure 205 by means of the time element PT1 220. At time 305, the intersection of the actual boost pressure 225 and the fill-based target boost pressure 205 reduced by offset 250, the PT1 curve of the target boost pressure 210 begins. This curve leads the target boost pressure 210 from the value of the fill-based target boost pressure 205 minus the offset 250 back to the original, fill-based target boost pressure 205. The time constant 270 of the PT1 curve is preferably derived from the characteristic map 275.

[0032] The specified target boost pressure 210 overrides the fill-based target boost pressure 205. At time 310, both values ​​are identical. As soon as the fill-based boost pressure 205 minus the offset 205 equals the actual boost pressure 215 plus the defined value 230, a PT1 curve begins, which brings the actual boost pressure 215 towards the target value of the fill-based target boost pressure 205.

[0033] Fig. Figure 4 shows a charge-based target boost pressure 205 and an actual boost pressure 215 at a turbocharger 110 with conventional control. In this exemplary representation, time is plotted horizontally and boost pressure vertically. The scales and quantitative curves shown are purely illustrative. A first curve 405 reflects the charge-based target boost pressure 205, and a second curve 410 reflects the actual boost pressure 215. In a range 415, the second curve 410 exceeds the specified value of the first curve 405. The transition between the increase and the essentially constant maintenance of the actual boost pressure 410, 215 appears uneven.

[0034] Fig. Figure 5 shows a corresponding representation for control using method 200. Fig.2. A curve 505 shows the deviating behavior of the procedure 200, caused by the offset 250 and the temporarily activated timer 220, as the actual boost pressure 215 approaches the fill-based target boost pressure 205. The curve 505 temporarily reduces the specified target boost pressure 210 to allow the actual boost pressure 215 to smoothly approach the fill-based target boost pressure 205. An overshoot of the actual boost pressure 215 above the fill-based target boost pressure 205 can be avoided. Nevertheless, a rapid increase in the actual boost pressure 215 occurs. 100 Powertrain 105 Internal combustion engine 110 turbochargers 115 Exhaust gas turbine 120 compressors 125 Engine control 130 Device 135 first interface 140 second interface 145 third interface 150 fourth interface 155 Speed ​​sensor 200 procedures 205 filling-based target boost pressure 210 Target boost pressure 215 Actual boost pressure 218 rpm 220 First-order time element 225 actual boost pressure carried 230 value 235 Determine the gradient of the fill-based target boost pressure 205 240 Determine the gradient of the actual boost pressure 215 245 Characteristic map (second according to claims) 247 Sum 250 Offset 255 Characteristic map (first according to claims) Subtract 260 265 Compare 270 time constant 275 Characteristic map (third according to claims) 280 Difference between 205 and 250 290 Addition of 220 and 280 305 Time Start PT1 310 Time of new target boost pressure 210 = filling-based target boost pressure 205 405 first curve (fill-based target boost pressure) 410 second curve (actual boost pressure) 415 area 505 Progression of the new target boost pressure 210

Claims

[1] Method (200) for controlling a target boost pressure (210) for a turbocharger (110) driven by exhaust gas of an internal combustion engine (105), wherein the method (200) comprises the following steps: - Determining (205) a filling-based target boost pressure (205) based on a filling of the internal combustion engine (105); - Sampling (215) of an actual boost pressure (215); - Determine (235, 245, 247) a carried actual boost pressure (225) based on the actual boost pressure (215); - Determining (255) an offset (250) based on the fill-based target boost pressure (205); and - Control (220) of the target boost pressure (210) by means of a first-order timer (220) to the filling-based target boost pressure (205), - if the actual boost pressure (225) exceeds a value (265) that is smaller by the offset (250) than the target boost pressure (205) based on the filling. [2] Method (200) according to claim 1, wherein the offset (250) is determined on the basis of the filling-based target boost pressure (205) and a rotational speed (218) of the internal combustion engine (105). [3] Method (200) according to claim 2, wherein the offset (250) is determined by means of a first characteristic map (255). [4] Method (200) according to one of the preceding claims, wherein the carried actual boost pressure (225) is determined on the basis of the sum (247) of the actual boost pressure (215) and a value (230) which is determined on the basis of the filling-based target boost pressure (205) and the actual boost pressure (215). [5] Method (200) according to claim 4, wherein the value (230) is determined on the basis of gradients (235, 240) of the filling-based target boost pressure (205) and the actual boost pressure (215). [6] Method (200) according to claim 4 or 5, wherein the value (230) is determined by means of a second characteristic map (245). [7] Method (200) according to one of the preceding claims, wherein a time constant (270) of the time element (220) is determined on the basis of the filling-based target boost pressure (205) and the actual boost pressure (215). [8] Method (200) according to claim 7, wherein the time constant (270) is determined on the basis of gradients (235, 240) of the filling-based target boost pressure (205) and the actual boost pressure (215). [9] Method (200) according to claim 7 or 8, wherein the time constant (270) is determined by means of a third characteristic map (275). [10] Device (130) for controlling a target boost pressure (210) for a turbocharger (110) driven by exhaust gas of an internal combustion engine (105), wherein the device (130) comprises: - a first interface (135) for determining a filling-based target boost pressure (205); - a second interface (140) for scanning an actual boost pressure (215); and - a processing facility that is equipped to, o to determine a carried actual boost pressure (225) based on the actual boost pressure (215); to determine an offset (250) based on the fill-based target boost pressure (205); and ◯ to control the target boost pressure (210) by means of a first-order timer (220) to the filling-based target boost pressure (205), ◯ if the actual boost pressure (225) exceeds a value that is less than the target boost pressure (205) based on the offset (250).

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