GB2517427A

GB2517427A - Method of controlling a waste gate valve of a turbocharger

Info

Publication number: GB2517427A
Application number: GB1314790.5A
Authority: GB
Inventors: Gerhard Landsmann; Baris Camurtay; Jorg Bernards
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2013-08-19
Filing date: 2013-08-19
Publication date: 2015-02-25
Anticipated expiration: 2033-08-19
Also published as: GB2517427B; GB201314790D0

Abstract

Disclosed is a method of controlling a waste gate valve 290 for a turbocharger 230 of an internal combustion engine 110, the waste gate valve comprising a waste gate actuator 295. The method performs the steps of determining a target value of the duty cycle of a pulse width modulated signal, estimating a pressure drop as a function of a current value of the duty cycle and said target value of the duty cycle and determining a duty cycle step as a function of said pressure drop. A transient value of the duty cycle of the pulse width modulated signal is determined, wherein said transient value corresponds to the current value of the duty cycle reduced by the duty cycle step. A time interval is determined and the transient value of the duty cycle of the pulse width modulated signal is applied to the waste gate actuator 295 during said time interval after which the target value of the duty cycle of the pulse width modulated signal is applied. The method results in applying a fictitious larger pressure step for a duty cycle of a waste gate control valve as it opens, resulting in a rapid response time.

Description

METHOD OF CONTROLLING A WASTE GATE VALVE OF A TURBOCHARGER

TECHNICAL FIELD

The present disclosure relates to a method of controlling a waste gate valve of a turbocharger, particularly a vacuum actuated waste gate. The method is suitable for internal combustion engines, and in particular is an enabler for using vacuum actuators, controlled by an electric pressure valve (or vacuum control valve, hereafter also simply EPV), in gasoline turbocharged engines, as already used in diesel engines.

BACKGROUND

is As known, the majority of internal combustion engines are tucbotharged. A turbocharger, is a forced induction device used to allow more power to be produced for an engine of a given size. The benefit of a turbo is that it compresses a greater mass of intake air into the combustion chamber, thereby resulting in increased power and/or efficiency.

Turbochargers are commonly used on truck, car, train and construction equipment engines. They are popularly used with Otto cycle and Diesel cycle internal combustion engines and have also been found useful in automotive fuel cells.

As also known, a turbocharged engine system utilizes a waste gate valve, which is a valve that diverts exhaust gases away from the turbine. Diversion of exhaust gases regulates the turbine speed, which in turn regulates the rotating speed of the compressor. The primary function of the waste gate is to regulate the maximum boost pressure in turbocharger systems, to protect the engine and the turbocharger. The waste gate valve is controlled by an internal combustion engine controller (for example an electronic control unit or ECU). A possible way to manage the waste gate is via a waste gate actuator also called vacuum control valve or electric pressure valve (EPV). This valve is electrically actuated by the ECU via a pulse width modulated signal (PWM), expressed as a duty cycle (DC) in percentage. As known, pulse width modulated (PWM) is a modulated technique that conforms the width of the pulse, formally the pulse duration, based on a modulator signal information. The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is. The term duty cycle describes the proportion of on' time to the regular interval or period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. As mentioned, duty cycle is normally expressed in percent, 100% being fully on. Hereafter the term "duty cycle" will always indicate a percentage value.

The EPV determines the vacuum pressure of the air, which is fed by a vacuum pump.

This negative air pressure (vacuum force) pushes against the force of a spring located in the waste gate actuator. The spring force allows the waste gate to open and re-direct exhaust gas so that it does not reach the turbine wheel, while the vacuum force realizes the closing of the waste gate.

It has to be observed, that the EPV for vacuum control has a good transient characteristic, in case of duty cycle big steps. For duty cycle step is meant a sudden change of the duty cycle, both a duty cycle increase and a duty cycle reduction. A duty cycle big step can be, for example, a sudden change from 20% to 50%. On the contrary, in case of duty cycle small steps and in particular when the duty cycle value is reduced (for example, a change from 20% to 15%), the waste gate transient characteristic makes waste gate opening control extremely slow. Of course, this impacts boost pressure control and might generate overboost or boost oscillations.

Therefore a need exists for a method of controlling a turbocharger waste gate valve of an internal combustion engine, aimed to improve its transient operation.

An object of an embodiment of the invention is to provide a method of controlling a turbocharger waste gate valve of an internal combustion engine, in particular, the method has to improve the transient behavior of the waste gate actuator, when it has to perform small openings due to a small reduction of the duty cycle of a PWM signal.

Another object is to provide an apparatus which allows to perform the above method.

These objects are achieved by a method, by an apparatus, by an engine, by a computer program and computer program product having the features recited in the independent claims.

The dependent claims delineate preferred andFor especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of controlling a waste gate valve for a turbocharger of an internal combustion engine, the waste gate valve comprising a waste gate actuator, wherein the method performs the following steps: -determining a target value of the duty cycle of a pulse width modulated signal, -estimating a pressure drop as a function of a current value of the duty cycle and said target value of the duty cycle, -determining a duty cycle step as a function of said pressure drop, -determining a transient value of the duty cycle of the pulse width modulated signal, wherein said transient value corresponds to the current value of the duty cycle, reduced by said duty cycle step, -determining a time interval, -applying to the waste gate actuator said transient value of the duty cycle of the pulse width modulated signal during said time interval, and after -applying to the waste gate actuator the target value of the duty cycle of the pulse width modulated signal.

Consequently, an apparatus is disclosed for performing the method of controlling a waste gate valve for a turbocharger of an internal combustion engine, the apparatus comprising: -means for determining a target value of the duty cycle of a pulse width modulated signal, -means for estimating a pressure drop as a function of a current value of the duty cycle and said target value of the duty cycle, -means for determining a duty cycle step as a function of said pressure drop, -means for determining a transient value of the duty cycle of the pulse width modulated signal, wherein said transient value corresponds to the current value of the duty cycle, reduced by said duty cycle step, -means for determining a time interval, -means for applying to the waste gate actuator said transient value of the duty cycle of the pulse width modulated signal during said time interval, and after -means for applying to the waste gate actuator the target value of the duty cycle of the pulse width modulated signal.

An advantage of this embodiment is that the method improves the transient behavior of the waste gate actuator, when it has to perform a small opening increase due to a small reduction of the duty cycle of the PWM signal. The improvement is realized by estimating a fictitious bigger step of the duty cycle of the PWM signal. For fictitious bigger step is meant a duty cycle difference bigger than the difference between the start value and the target value of the duty cycle, which should be applied. Then a transient value of the duty cycle (which is the start value reduced by said fictitious bigger step) is applied during a predetermined time interval and finally the target value of the duty cycle of the PWM signal is applied. In this way, the overall time, needed by the waste gate actuator to get the desired position of the waste gate valve, is remarkably reduced.

According to another embodiment, said pressure drop is estimated by using a steady state model of the waste gate actuator and is utilized as an input parameter of a transient model of the waste gate actuator.

Consequently, said means for estimating a pressure drop are configured to use a steady state model of the waste gate actuator and the pressure drop is utilized as an input parameter of a transient model of the waste gate actuator.

An advantage of this embodiment is that said pressure drop, estimated by the steady state model of the waste gate actuator, can be used as an input parameter in a transient model of the waste gate actuator, to provide the fictitious bigger step of the duty cycle and the time interval during which said duty cycle step shall be applied.

According to a still further embodiment, said duty cycle step, which is a function of said pressure drop, is estimated by using the transient model of the waste gate actuator.

Consequently, said means for determining a duty cycle step, which is a function of said pressure drop, are configured to use the transient model of the waste gate actuator.

An advantage of this embodiment is that for each value of the pressure drop, the transient model provides a corresponding value of the fictitious bigger step of the duty cycle.

According to still another embodiment, said time interval is a function of said duty cycle step of the pulse width modulated signal and is estimated by using the transient model of the waste gate actuator.

Consequently, said means for determining a time interval are configured to calculate said time interval as a function of said duty cycle step of the pulse width modulated signal, by using the transient model of the waste gate actuator.

An advantage of this embodiment is that for each value of the fictitious bigger step of the duty cycle of the PWM signal, the transient model provides a corresponding value of the time interval during which said duty cycle step of the PWM signal has to be used or, better, said transient value of the duty cycle is applied.

Another embodiment of the disclosure provides an internal combustion engine comprising a turbocharger and a waste gate valve, wherein the waste gate valve is controlled by a method according to any of the preceding claims.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program product can be embedded in a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are canied out.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system.

Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is a schematic overview of a turbocharged internal combustion engine.

Figure 4 shows the different dynamic behaviors of the vacuum waste gate actuator.

Figure 5 shows the waste gate actuator response to PWM signal changes.

Figure 6 is a flowchart of the method according to an embodiment of the present invention.

Figure 7 shows the interaction between a steady-state model and a transient model used in an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190.

Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200.

An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a fixed geometry turbine 250 including a waste gate 290. In other embodiments, the turbocharger 230 may be a variable geometry turbine (VOT) with a VGT actuator arranged to move the vanes to alter the flow of the exhaust gases through the turbine.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and equipped with a data carrier 40. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow, pressure, temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the waste gate actuator 290, and the cam phaser 155.

Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interlace bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interlace bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interlace bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices.

The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

The program stored in the memory system is transmitted from outside via a cable or in a wireless fashion. Outside the automotive system 100 it is normally visible as a computer program product, which is also called computer readable medium or machine readable medium in the art, and which should be understood to be a computer program code residing on a carrier, said canier being transitory or non-transitory in nature with the consequence that the computer program product can be regarded to be transitory or non-transitory in nature.

An example of a transitory computer program product is a signal, e.g. an electromagnetic signal such as an optical signal, which is a transitory carrier for the computer program code. Carrying such computer program code can be achieved by modulating the signal by a conventional modulated technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electromagnetic signal. Such signals are e.g. made use of when transmitting computer program code in a wireless fashion via a VViFi connection to a laptop.

In case of a non-transitory computer program product the computer program code is embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrievable way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an Asic, a CD or the like.

Instead of an ECU 450, the automotive system 100 may have a different type of processor to provide the electronic logic, e.g. an embedded controller, an onboard computer, or any processing module that might be deployed in the vehicle.

Figure 3 is a schematic overview of a turbocharged internal combustion engine. In the scheme, other than the compressor 240 and the turbine 250, is shown the waste gate valve 290 and the electric pressure valve (EPV) 295, i.e. the waste gate actuator. The EPV determines the vacuum pressure of the air, which is fed by a vacuum pump. This negative air pressure or controlled vacuum 510 pushes against the force of a spring 500 located in the waste gate valve 290. The force scheme is shown on the bottom right of the same picture: at the spring force 550 is opposed a variable vacuum force 560. The resulting force acts on a membrane 520, which, due to its strain, moves a waste gate rod 540 up and down, allowing the waste gate valve to open and re-direct exhaust gases, so that they do not reach the turbine wheel, or to close, let the exhaust gases flowing through the turbine 250. A rod position sensor 530 can be used to control the position of the waste gate rod.

The functioning of the waste gate control and the related issue which is solved by the present method are shown in Fig. 4. To regulate the maximum boost pressure 600, the ECU controls the waste gate valve 290 via a PWM signal 610 to the electric pressure valve (or waste gate actuator) 295. The EPV determines the vacuum pressure of the air and consequently the opening/closing of the waste gate valve by means of the waste gate rod 540 movement. Its movement 620 is monitored by the rod position sensor 530.

It can be observed that, the EPV for vacuum control has a good transient characteristic (i.e. the waste gate rod movement 621 due to a change of the duty cycle of the PWM signal), when responding to big changes (big steps) of the duty cycle of the PWM signal 611: the response is very fast and the opening/closing of the waste gate follows quite well the change of the duty cycle of the PWM signal. Similar situation can be observed in case of small increase of the duty cycle of the PWM signal 612, since the waste gate rod movement 622 due to a small increase of the duty cycle of the PWM signal 622 is very fast as well. On the contrary, in case of a small reduction of the duty cycle of the PWM signal 613, the transient characteristic makes the waste gate opening control extremely slow, as the behavior of the waste gate rod movement 623 (see Fig. 4), due to a small reduction of the duty cycle, makes clear. In conclusion, the vacuum actuator behavior, in case of small reductions of the duty cycle of the PWM signal, implies different dynamics for the waste gate opening and closing and, in particular, an undesired behavior for the waste gate opening.

Figure 5 shows in greater detail the latter case, i.e. the slow actuator reaction to a small reduction of the duty cycle of the PWM signal. In such figure, several cases are simulated in the graph representing the waste gate vacuum pressure as a function of the time. Hereafter, pressure is always to be understood as vacuum pressure, that is to say, pressure values always lower than the atmospheric pressure value. Each curve represents the behavior of the waste gate vacuum pressure, better the actuator rod position, during the time due to a different small reduction of the duty cycle of the PWM signal. In particular, in the example, all three curves start with a DC = 31%, while the final DC value is respectively 20%, 17% and 15%. It can be seen that the vacuum pressure behavior follows a transient behavior 700', 700", 700" up to a transient point 705', 705", 705'" and this transient behavior is quite acceptable (the belier the bigger step of the duty cycle of the PWM signal); then the behavior is still transient 710', 710", 710" but very slow (the better the smaller step of the duty cycle of the PWM signal) up to a steady state point 715', 715", 715'". Finally the curve becomes horizontal, that is to say the waste gate vacuum pressure has reached its desired steady state value 720', 720", 720". It follows that, for a given duty cycle step of the PWM signal, there will be a fictitious bigger step of the duty cycle of the PWM signal, which would provide a faster transient behavior of the waste gate vacuum pressure up to the transient point; moreover, for a given duty cycle step of the PWM signal, there will be a transient point 705" (corresponding to a bigger step of the duty cycle of the PWM signal) having the same vacuum pressure value of the steady state point 715', corresponding to the desired waste gate vacuum pressure for the given duty cycle step of the PWM signal. For example, following the numerical values as in Fig. 5, for a given duty cycle step (11% = 31% -20%), there will be a fictitious bigger step of the duty cycle (14% = 31% -17%), which would provide a faster transient behavior of the waste gate vacuum pressure up to the transient point 705" and this transient point 705" has the same vacuum pressure value of the steady state point 715' corresponding to the desired waste gate vacuum pressure for the given duty cycle step (11%) of the PWM signal.

In Fig. 6 and 7 a preferred embodiment of the method is illustrated. Fig. 6 is a flow chart describing the method and Fig. 7 comprises two graphs. In Fig. 7a an empirical steady state model of the waste gate actuator 295 is described, while Fig. 7b shows an empirical transient model of waste gate actuator 295. Such models are built, as an example, by averaging the behavior of a significant batch of waste gate actuators. As will appear soon after, Fig. 6 and 7 are extremely interconnected and for sake of clarity they will be described together. In Fig. 7a, a curve 900 represents a steady state model of the waste gate actuator, correlating the vacuum pressure behavior [kPaj as a function of the duty cycle of the PWM signal. In other words, this model estimates the vacuum pressure value, the waste gate actuator will provide for a given duty cycle of the PWM signal. Of course, the lower the duty cycle of the PWM value, the lower the vacuum pressure value.

Fig. 7b shows a transient model of the waste gate actuator in terms of vacuum pressure drop (curve 910) versus duty cycle step of the PWM signal and transient time (curve 920) versus duty cycle step of the PWM signal.

The method performs the steps of the flowchart, as in Fig. 6. At first, the method will use a current value PWMstr of the duty cycle of the PWM signal. Moving to Fig. 7a, let us suppose, as an example, 25% as current value PWMstr of the duty cycle, which, according to the steady state model (curve 900) will provide a certain pressure value, in the example 15.7 kPa. Then, the target value PWMtgt of the duty cycle of the PWM signal is determined S810. In Fig. 7a, showing the steady state model, this point is referenced as PWMtgt and, for example, corresponds to a duty cycle value of 20%. At this target value, according to the steady state model, corresponds a lower pressure value, 11 kPa in the example. Therefore, the duty cycle reduction, which has to be actuated, is 5% (25%-20%). A correspondent pressure drop Ap can be estimated S820, according to the steady-state model, in this case 15.7-11 = 4.7 kPa.

Then, the method determines S830 a duty cycle step APWMtr (better, a bigger fictitious step) of the PWM signal from the transient model (shown Fig. 7b). Such step APWMtr is a function of the same pressure drop Ap, as estimated from the steady state model. In this example, the difference of the duty cycle of the PWM signal is 10%, as expected, bigger than the imposed duty cycle step (5%), which has to be performed. Consequently, a transient value PWMtr of the duty cycle can be calculated S840 and it corresponds to the start value PWMstr of the duty cycle, reduced by the duty cycle step APWMtr, i.e.: PWMtr = PWMstr -APWMtr Always from the transient model, using the transient time curve 920, a time interval At, as a function of the estimated duty cycle step APWMtr of the PWM signal can be determined S850 (in the example, the time interval At corresponds to 30 ms). Therefore, the bigger step of the duty cycle APWMtr of the PWM signal (10% instead of 5%) and the time interval At, during which the duty cycle step APWMtr has to be utilized, are now available. Finally, according to the method, this duty cycle said is used, in other words, the transient value of the duty cycle is applied 860 to the solenoid valve during the time interval At. Finally, after the transient time At is expired, the target value PWMtgt of the duty cycle of the PWM signal is applied 8870.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

data carrier automotive system 110 internal combustion engine engine block cylinder cylinder head camshaft 140 piston crankshaft combustion chamber cam phaser fuel injector 165 fuel injection system fuel rail fuel pump fuel source intake manifold 205 air intake duct 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 290 waste gate valve 295 waste gate actuator or electric pressure valve or boost pressure control valve 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow, pressure, temperature and humidity sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 350 coolant temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail digital pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 500 waste gate spring 510 controlled vacuum 520 membrane 530 rod position sensor 540 waste gate rod 550 spring force 560 variable vacuum force 600 boost pressure or manifold pressure 610 PWM signal (duty cycle %) 611 big increase of the duty cycle of the PWM signal 612 small increase of the duty cycle of the PWM signal 613 small reduction of the duty cycle of the PWM signal 620 waste gate rod movement 621 waste gate rod movement due to a big increase of the duty cycle of the PWM signal 622 waste gate rod movement due to a small increase of the duty cycle of the PWM signal 623 waste gate rod movement due to a small reduction of the duty cycle of the PWM signal 700 vacuum fast transient behavior 705 vacuum behavior transient point 710 vacuum slow transient behavior 715 vacuum behavior steady state point 720 vacuum steady state behavior S810 step S820 step S830 step S840 step S850 step S860 step S870 step 900 pressure vs. duty cycle of the pulse width modulated signal (curve of the steady state model) 910 pressure drop vs. duty cycle step of the pulse width modulated signal (curve of the transient model) 920 time interval vs. duty cycle step of the pulse width modulated signal (curve of the transient model) PWMstr current value of the duty cycle of the pulse width modulated signal PWMtgt target value of the duty cycle of the pulse width modulated signal Ap pressure drop APWMtr duty cycle step of the pulse width modulated signal PWMtr transient value of the duty cycle of the pulse width modulated signal time interval

Claims

CLAIMS1. Method of controlling a waste gate valve (290) for a turbocharger (230) of an internal combustion engine (110), the waste gate valve comprising a waste gate actuator (295), wherein the method performs the following steps: -determining a target value (PWMtgt) of the duty cycle of a pulse width modulated signal, -estimating a pressure drop (Ap) as a function of a current value (PWMstr) of the duty cycle and said target value (PWMtgt) of the duty cycle, -determining a duty cycle step (APWMtr) as a frmnction of said pressure drop (Ap), -determining a transient value (PWMtr) of the duty cycle of the pulse width modulated signal, wherein said transient value (PWMtr) corresponds to the current value (PWMstr) of the duty cycle, reduced by said duty cycle step (APWMtr), -determining a time interval (At), -applying to the waste gate actuator (295) said transient value (PWMtr) of the duty cycle of the pulse width modulated signal during said time interval (At), and after -applying to the waste gate actuator (295) the target value (PWMtgt) of the duty cycle of the pulse width modulated signal.
2. Method according to claim 1, wherein said pressure drop (Ap) is estimated by using a steady state model of the waste gate actuator (295) and is utilized as an input parameter of a transient model of the waste gate actuator (295).
3. Method according to claim 1 or 2, wherein said duty cycle step (aPWMtr), which is a function of said pressure drop (Ap), is estimated by using the transient model of the waste gate actuator (295).
4. Method according to claim 1, wherein said time interval (At) is a function of said duty cycle step (APWMtr) of the pulse width modulated signal and is estimated by using the transient model of the waste gate actuator (295).
5. Internal combustion engine (110) comprising a turbocharger (230) and a waste gate valve (290), wherein the waste gate valve is controlled by a method according to any of the preceding claims.
6. A non-transitory computer program comprising a computer-code suitable for performing the method according to any of the claims 1-4.
7. Computer program product on which the non-transitory computer program according to claim 6 is stored.
8. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a non-transitory computer program according to claim 6 stored in a memory system (460).