GB2501922A

GB2501922A - Method of controlling a two-stage turbocharger system

Info

Publication number: GB2501922A
Application number: GB1208260.8A
Authority: GB
Inventors: Martin Miertschink; Francesco Castorina; Paolo Nalbone
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-05-10
Filing date: 2012-05-10
Publication date: 2013-11-13
Anticipated expiration: 2032-05-10
Also published as: GB201208260D0; GB2501922B

Abstract

Disclosed is a method of controlling a two-stage turbocharger system for an internal combustion engine equipped with an intake manifold 200. The two-stage turbocharger comprises a first turbocharger 250 and a second turbocharger 550, the second turbocharger 550 operating at a lower pressure than the first turbocharger 250, and a plurality of regulating devices for varying a flow of engine exhaust gas in the two-stage turbocharger system. The regulating devices may be a variable geometry turbo, waste valves or exhaust bypass valves. The method comprises the steps of determining the pressure in the intake manifold, determining a target value for the pressure on the basis of an engine operating point, determining a value of a control variable for the two-stage turbocharger as a function of the difference between the determined pressure and the target pressure, selecting one of the regulating devices on the basis of the determined value of the control variable and actuating the selected regulating device. More than one of the regulating devices can be used when the pressure is high. An internal combustion engine having an engine controller 450 programmed with software to carry out the method is also disclosed.

Description

METHOD OF CONTROLL/NG A TWO-STAGE TURBOCHARGER OF AN INTERNAL

COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of controlling a two-stage turbocharger of an internal combustion engine.

BACKGROUND

Automotive engine systems may comprise an internal combustion engine equipped with an intake manifold and an exhaust manifold.

Internal combustion engines may be equipped with turbochargers comprising a turbine which rotates a compressor through a connecting shaft in order to charge air into the intake manifold at increased pressure.

Internal combustion engines, in particular but not exclusively Diesel engines, may be equipped with two-stage turbocharger systems that comprise two sequential turbochargers which are selectively operated in accordance with engine speed and engine load.

These two-stage systems comprise a high-pressure turbocharger and a low-pressure turbocharger, both having a compressor and a turbine.

The compressor of the high-pressure turbocharger is located in the intake line downstream the compressor of the low-pressure turbocharger, relative to the flow direction.

The intake line comprises a low-pressure intake line for fluidly connecting the outlet of low-pressure compressor to the inlet of high-pressure compressor, and a high-pressure intake line for fluidly connecting the outlet of high-pressure compressor to the intake manifold. Between the outlet of high-pressure compressor and the intake manifold, a cooler device is generally provided for cooling airflow before entering the intake manifold.

The high pressure turbine may be a variable geometry turbine (VGT), namely a turbine that is equipped with a ring of aerodynamically-shaped vanes enclosed in the turbine housing at (he turbine inlet.

By rotating the vanes in unison the gas swifl angle and the cross sectional area or aspect ratio of the turbine can be regulated.

At low engine speeds when exhaust flow is low, the vanes are partially closed. This increases the pressure before the turbine and leads to an increasing speed of the exhaust flow, making the turbine spin faster and generating more boost. As engine speed increases, so does exhaust flow, so the vanes are opened to reduce turbine pressure and hold boost steady or reduce it as needed.

The high pressure turbine may be also associated with a by-pass valve for allowing exhaust gas from the engine to by-pass the high pressure turbine.

The low pressure turbine may be provided with a wastegate namely a valve that diverts exhaust gases away from the turbine wheel in order to regulate the maximum boost pressure in the low pressure turbine, in particular to protect the engine and the turbocharger.

The intake line may also comprise a bypass device arranged for allowing the airflow to bypass the high-pressure compressor when the high-pressure turbocharger is disabled.

The two turbochargers are arranged such that at Low engine speeds both turbochargers are used for charging air into the engine, while as engine speed increases, the high-pressure turbocharger is gradually disabled.

Therefore the two-stage turbocharger may be actuated by means of three actuators, namely the variable geometry turbine (VOT), the high pressure turbine bypass (HPT Bypass) and the wastegate!G) of the low pressure turbine.

An Electronic Control Unit (ECU) that manages the various functions of the automotive system, is also employed to control these actuators in closed loop, for example by employing a proportional-integral--derivative controller (PlO controller) that receives as feedback a pressure signal from a pressure sensor in the intake manifold.

However, since there are three actuators to control, the ECU must manage three different closed loop controls.

This fact has the costly consequence that three different PIDs must be each calibrated in order to achieve the desired control leading to a high calibration effort and the need for a dedicated software tool.

An aim of an embodiment of the present invention is to simplify the control of the two-stage turbocharger system.

An aim of an embodiment of the present invention is to improve the ease and to reduce the time of the calibration process for a two-stage turbocharger system.

Another object an embodiment of the present invention is to provide a two-stage turbocharger control strategy without using complex devices and by taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle.

Still another aim of an embodiment of the present invention is to meet these and other goals with a rather simple, rational and inexpensive solution.

The dependent claims delineate preferred and/or especiafly advantageous aspects.

SUMMARY

An embodiment of the invention provides a method of controlling a two-stage turbocharger system of an internal combustion engine comprising a plurality of regulating devices for varying a flow of engine exhaust gas in the two-stage turbocharger system, the method comprising the steps of: -determining a value of a parameter representative of a pressure in an intake manifold, -determining a target value of the parameter on the basis of an engine operating point, -determining a value of a control variable for the two-stage turbocharger as a function of the difference between the determined value of the parameter and the target value thereof, -selecting one of the regulating devices on the basis of the determined value of the control variable, -actuating the selected regulating device.

The two-stage turbocharger may comprise a first and a second turbocharger, the second turbocharger operating at a lower pressure than the first turbocharger.

An advantage of this embodiment is that it allows to control the operations of a two-stage turbocharger system using a single closed loop control and, therefore, reducing the complexity of the calibrations that are necessary with prior art control strategies.

Furthermore, this embodiment of the invention allows to avoid a time consuming and costly calibration process, because the method allows to calculate correct request for each actuator depending on the PlO for each engine operating point.

Moreover, when one of the actuators of the two-stage turbocharger system is moved, the other actuators are set in fixed position.

This allows to switch from one actuator to the next in sequence in order respectively, to build up pressure in the manifold orto discharge it.

According to an embodiment of the invention, the set of ranges of values of the two-stage turbocharger system control variable are ordered in such a way to define a first sequence of actuation of the actuators for increasing pressure in the intake manifold and second sequence of actuation of the actuators for decreasing pressure in the intake manifold.

An advantage of this embodiment is that it allows to predefine the condition to operate the two-stage turbocharger to build up or to discharge pressure according to the needs.

Another embodiment of the method of the invention, comprises a step of increasing pressure in the intake manifold if the determined value of the parameter is lower than the desired value thereof, the pressure increase being generated by actuating the determined actuator until a maximum allowed closed position.

An advantage of this embodiment is that it allows to perform a pressure build up using only one actuator.

According to another embodiment of the method of the invention, if the actuated actuator reaches the maximum allowed closed position before the desired value of the parameter is obtained, the intake manifold pressure increase is continued by actuating the subsequent actuator in the first sequence.

An advantage of this embodiment is that it allows to continue a pressure build up switching to the more suitable actuator depending on the engine operating point.

Still another embodiment of the method of the invention comprises a step of decreasing pressure in the intake manifold if the determined value of the parameter is higher than the desired value thereof, the pressure decrease being generated by actuating the determined actuator until a minimum allowed open position.

An advantage of this embodiment is that it allows to perform a pressure discharge using only one actuator.

According to another embodiment of the method of the invention, if the actuated actuator reaches the minimum allowed open position before the desired value of the parameter is obtained, the intake manifold pressure decrease is continued by actuating a subsequent actuator in the second sequence.

An advantage of this embodiment is that it allows to continue a pressure discharge up switching to the more suitable actuator depending on the engine operating point.

According to an embodiment of the invention, the actuator actuated is a wastegate valve of a low-pressure turbine of the low-pressure turbocharger.

According to an embodiment of the invention, the actuator actuated is a high pressure turbine bypass valve of a high-pressure turbine of the high-pressure turbocharger.

According to an embodiment of the invention, the actuator actuated is a variable geometry turbine of the high-pressure turbocharger.

Another embodiment of the invention provides an apparatus for operating a two-stage turbocharger system for an internal combustion engine comprising a plurality of regulating devices for varying a flow of engine exhaust gas in the two-stage turbocharger system, the apparatus comprising: -means for determining a value of a parameter representative of a pressure in an intake manifold, -means for determining a target value of the parameter on the basis of an engine operating point, -means for determining a value of a control variable for the two-stage turbocharger as a function of the difference between the determined value of the parameter and the target value thereof, -means for selecting one of the regulating devices on the basis of the determined value of the control variable, -means for actuating the selected regulating device.

Another embodiment of the invention provides an automotive system comprising an internal combustion engine equipped with a two-stage turbocharger system comprising a plurality of regulating devices for varying a flow of engine exhaust gas in the two-stage turbocharger system, the automotive system being managed by an electronic control unit configured to: -determine a value of a parameter representative of a pressure in an intake manifold, -determine a target value of the parameter on the basis of an engine operating point, -determine a value of a control variable for the two-stage turbocharger as a function of the difference between the determined value of the parameter and the target value thereof, -select one of the regulating devices on the basis of the determined value of the control variable, -actuate the selected regulating device.

These last two embodiments have the same advantages of the method disclosed above.

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 embodied as 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 carried out.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

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 cross-section of an internal combustion engine belonging to the automotive system of figure 1; Figure 3 is a schematic representation of a two-stage turbocharger system that employs the various embodiments of the invention; Figure 4 is a schematic representation of the main steps of a first embodiment of the inventive method; Figure 5 is a schematic representation of the main steps of a second embodiment of the inventive method; Figure 6 is a graph representing the position of a wastegate valve of a low-pressure turbine as a function of a two-stage turbocharger control variable; Figure 7 is a graph representing the position of a high pressure turbine bypass valve as a function of a two-stage turbocharger control variable; Figure 8 is a graph representing the position of a set of vanes of a variable geometry turbine as a function of a two-stage turbochargercontrol variable; Figure 9 is a graph that combines the representations of figures 6-8; and Figure lOis a schematical representation of the overall structure of an embodiment of the method of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will now be described with reference to the enclosed drawings without intent to limit application and uses.

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 at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increases 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 an intake 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 intake line 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 two-stage turbocharger system 500 may be provided.

In fig. 3 a two-stage turbocharger system 500 is described in more detail, the two- stage turbocharged system 500 comprising a high-pressure turbocharger 505 and a low-pressure turbocharger 507, both having a compressor and a turbine.

The compressor 240 of the high-pressure turbocharger 505 is located in the intake line 205 downstream the compressor 540 of the low-pressure turbocharger 507 *relative to the flow direction.

The outlet of the low-pressure compressor 540 may be connected to the inlet of the high-pressure compressor 240.

A high-pressure intake line 207 is provided for fluidly connecting the outlet of the high-pressure compressor 240 to the inlet of an intercooler device 260, the intercooler device being suitable for cooling airflow before entering the intake manifold 200.

The high pressure turbine 250 may be a variable geometry turbine (VGT), namely a turbine that is equipped with include a ring of aerodynamically-shaped vanes in the turbine housing at the turbine inlet. An actuator 290 may be operated in order to rotate the vanes in unison to regUlate the gas swirl angle and the cross sectional area or aspect ratio of the turbine.

The high pressure turbine 250 may be associated with a high pressure turbine by-pass valve 510 (HPT valve) for allowing exhaust gas from the engine 110 to by-pass the high pressure turbine 250.

A low pressure turbine 550 is be provided with a wastegate 520, namely a valve that diverts exhaust gases away from the turbine wheel in a turbocharged engine system in order to regulate the maximum boost pressure in the low pressure turbine 550, to protect the engine and the turbocharger.

The intake line may also comprise a bypass device 590 arranged for allowing the airflow to bypass the high-pressure compressor 240 when the high-pressure turbocharger is disabled.

Rotation of the compressors 240,540 increases the pressure and temperature of the air in the high-pressure intake line 207 and intake manifold 200. The intercooler 260 disposed in the high-pressure intake line 207 may reduce the temperature of the air. The turbines 250550 rotate 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 low pressure turbine 550 and are directed into an exhaust system 270. This example shows a high pressure variable geometry turbine (VGT) with a VOT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the high pressure turbine 250. In other embodiments, the high pressure turbine 250 may be of fixed geometry type.

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 include1 but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NO traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters.

Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200.

Another EGR system. (not represented for simplicity) could be coupled between the pipes after turbine and the pipe before compressor (low pressure EGR or long-route 83 R).

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.

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 and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 360, 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.

According to some embodiments of the invention, the ECU 450 may receive signals from the fuel injection system 600, as will be explained hereinafter.

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 VGT 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, or data carrier 460, and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals tolfrom 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.

According to an embodiment of the invention, the two-stage turbocharger system 500 is controlled by means of a sequential control strategy.

In particular, the two-stage turbocharger system 500 may be controlled by means of three actuators, namely the high pressure turbine bypass 510 (HPT Bypass), the wastegate 520 of the low pressure turbine (WG) and the variable geometry turbine (VGT) actuator 290, in order to vary the flow of engine exhaust gas in the two-stage turbocharger 500 system.

However, according to an embodiment of the invention, in any moment only one actuator 290,510,520 is moved and controlled in closed loop, while the other actuators are set in a fixed position depending on calibrated feedforward, until a switch is performed from a first actuator to a second actuator.

The switch between different actuators is performed in sequence, namely a first sequence of actuation of the actuators for increasing pressure in the intake manifold 200 and second sequence of actuation of the actuators for decreasing pressure in the intake manifold 200 may be defined.

A series of maps are stored in a data carrier 460 associated to the ECU 450, whereby each actuators range of positions is defined for each engine operating point.

In fact, for each actuator a map MAX (block 700) is defined, these maps containing the values of the maximum allowed closed positions MAXWG,MAXHPT,MAXVGT for each actuator as a function of the engine operating point.

The values MAXWG,MAXHPT,MAXVGT may correspond to a completely closed position of the actuator or, in certain cases, to maximum allowed positions for certain engine operating points in order to limit the authority of the control system, for example for safety reasons.

Furthermore, for each actuator a map MIN (block 720) is defined, these maps containing the values of the minimum allowed open positions MINWG,MINHPT,MINVGT for each actuator as a function of the engine operating point The values MlN,MlNHm-,MlNvGy may correspond to a completely open position of the actuator or, in certain cases, to minimum allowed positions for certain engine operating points in order to limit the authority of the control system, for example for safety reasons -Finally, for each actuator a map FeedForwa,d (block 710) is defined, these maps containing the values of feedforward positions FFWDWG,FFWDHFT,FFWDVGT for each actuator, namely values that may be used to feedforward control the actuators as a function of the engine operating point.

Therefore for each of the three actuators of the two-stage turbocharger system, three maps MAX1 MIN and FeedForward representing a range of actuator's positions as a function of engine operating points, are defined and stored in the data carrier 460.

The values of these maps may be determined by calibration by means of an experimental activity and are generally present in current two-stage turbocharger systems.

According to an embodiment of the invention, to each range of positions of each actuator is associated to a corresponding range of a two-stage turbocharger control variable PlO.

The values that the control variable PID may assume are therefore subdivided in a set of ranges of values, each range of values of the control variable PID being associated to a corresponding actuator 290,510,520.

Moreover, these sets of values are ordered in such a way to define a first sequence of actuation of the actuators for increasing pressure in the intake manifold 200 and second sequence of actuation of the actuators for decreasing pressure in the intake manifold 200.

For example, with reference to the figures 6-9, the values of the variable PID may be subdivided in a set of values from zero to a positive value Wpos and this set be associated to a closing movement of the wastegate 520.

Also the values of the variable PID from positive value WposwG to positive value WPOSHPT may be associated to a closing movement of the HPT bypass valve 510.

The values of the variable PID from positive value WposnpT to positive value WpOsVGT may be associated to a closing movement of the VTG turbine.

These first three sets are therefore also associated with a sequence of actuation for increasing pressure in the intake manifold 200.

The values of the variable PID may also be subdivided in a set of values from zero to a negative value Wnegwc and this set be associated to an opening movement of the wastegate 520.

Also the values of the variable PID from negative value Wnegwc to positive value WnegHpl may be associated to an opening movement of the HPT bypass valve 510.

The values of the variable PID from negative value Wnegp-r to negative value Wneg1 may be associated to an opening movement of the VTG turbine.

These second three sets are therefore associated to a sequence of actuation of the actuators for decreasing pressure in the intake manifold 200.

In general, each actuator has a positive position range that can be defined, for each actuator, i as: Positive range1 = Wpos = (MAX -FFWD1).

Also1 each actuator can have a negative position range that can be defined for each actuator i as: Negative range1 =Wneg1 = (MIN1-FFWD1) According to an embodiment of the invention, in order to implement the above phases, a parameter representative of a pressure in the intake manifold 200 is measured, for example by means of pressure sensor 350 or calculated by means of a model.

On the basis of the difference between the value of this parameter and a desired value thereof, the ECU 450 of the internal combustion engine 110 determines a value of a two-stage turbocharger 500 system control variable PID.

The PID value is then confronted with the ranges determined for each actuator and a decision about which actuator to move, while leaving the others in a fixed position, is made on the basis of the PID variable value.

For example if the PID value is greater than the values associated with the range of the wastegate 520, the actuator wastegate 520 is moved to its maximum allowed position, for example a closed position, and then the next actuator in sequence, that in this case is the HPT bypass valve 510 is actuated.

Also, for example, if the PID value is smaller than the values associated with the range of the VGT actuator 290, the VGT actuator 290 is moved to its minimum allowed position MINVGT for that engine operating point, for example a fully open position, and then the next actuator in sequence, that in this case is the I-PT bypass valve 510 is acted upon.

Figure 4 is a schematic representation of the main steps of an embodiment of the inventive method that refers to an exemplary full pressure build up in the intake manifold, starting with an open wastegate 520 position and then closing, in sequence, the various actuators 510,520290.

This may happen if the determined value of the pressure in the intake manifold 200 parameter is lower than the desired value thereof.

In this case the value of the control variable (PID) may be such that the wastegate 520 is selected first.

Therefore, to build up boost pressure, the wastegate (WG) 520 is closed first (block 600), then the bypass of the high pressure turbine (HPT) 510 is closed (block 610), and then the variable geometry turbine (VGT) is closed (block 620).

In particular, the wastegate may be operated starting from a feedforwarci position value FFWDWG up to a maximum value MAX in which the wastegate 520 is closed, then the high pressure turbine bypass valve (HPT) 510 is operated starting from a feedforward position value FFWDHPT up to a maximum value MAXHP-T-in which it is closed, and finally the variable geometry turbine (VGT) is actuated starting from a feedforward position value FFWDv01 up to a maximum value MAXVGT in which it is closed.

An advantage of this embodiment is that the feedforward position values FFWD,FFWDHn and FFWDVGT are already stored in the data carrier 460 and can be readily used by the ECU 450.

It is worthwhile to note that, when the wastegate 520 of the low pressure turbine is open and a pressure build up is requested, the wastegate 520 is closed before acting on the high pressure turbine (HPT) bypass valve because the HPT gain on manifold pressure when the wastegate 520 is open or partially open is very small.

When the HPT bypass 510 is open, it is closed before actuating the vanes of the variable geometry turbine (VGT), because the VGT gain on manifold pressure when the HPT valve is open is quite small Figure 5 is a schematic representation of the main steps of a second embodiment of the inventive method.

In this case, an exemplary decrease boost pressure is described.

The VOT is opened first (block 630) starting from the feedforward position value FFWDVGT up to a minimum value MINVOT in which it is fully open. Then HPT bypass valve 510 (block MO) is opened starting from a feedforward position value FFWDH up to a minimum value MINHPT in which it is fully open. Finally the wastegate 520 (block 650) is opened starting from a feedforward position value FFWDWG up to a minimum value MlN6 in which the wastegate 520 is fully open.

The reason for this sequence is that the actuator 290 of the VGT must be the first actuator to be moved otherwise, if the I-IPC bypass 510 is opened as a first actuator, after its opening, the VOT opening will not have any effect on manifold pressure.

In every condition is necessary to discharge to HP turbine before actuating the low pressure turbine wastegate 520, otherwise the high pressure turbine 250 can easily overspeed.

Figure 6 is a graph representing possible positions of the wastegate 520 of the low-pressure turbine as a function of the two-stage turbocharger control variable PID.

The range of values of the PlO variable from zero to WPOSWG are associated to positions of the wastegate 520 comprised between the feedforward value FFWDw and the value MAXWG which corresponds to a maximum allowable closed position of the wastegate 520.

The range of values of the PID variable from WnegHfl to WnegWG are associated to positions of the wastegate 520 Wneg6 defined between the value FFWD0 and a value MINWG which corresponds to a maximum allowable open position of the wastegate.

Figure 7 represents possible positions of the high pressure turbine (HPT) bypass valve as a function of the two-stage turbocharger control variable PID.

The range of values of the PID variable from Wpos,0 to WPOSHPT are associated to positions of the HPT bypass valve 510 comprised between the feedforward value FFWDIIPT and a value MAXRn to a maximum allowable closed position of the HPT bypass valve 510.

The range of values of the PID variable from Wnegv to Wne9HPT are associated to positions of the HPT bypass valve 510 comprised between the feedforward value FFWDpr and a value MINHPT which corresponds to a minimum allowable open position of the HPT bypass valve 510.

Figure 8 represents possible positions of the variable geometry turbine (VGT) vanes as a function of the two-stage turbocharger control variable PID.

The range of values of the PlO variable from WPOSHPT to WPOSVGT are associated to positions of the VGT vanes comprised between a feedforward value FFWDVGT and a value MAXVGT which corresponds to a maximum allowable closed position of the VGT vanes.

The range of values of the PID variable from zero to WnegVT are associated to positions of the VGT vanes comprised between a feedforward value FFWDVGT and a value MlNvcj-which corresponds to a minimum allowable open position of the VGT vanes.

In figure 9 the representations of figures 6-8 are combined together in order to show the sequences of actuations of the actuators, namely the right portion of the graph represents a full pressure build up sequence and the left portion of the graph represents a pressure discharge sequence.

Figure 10 is a schematical representation of the overall structure of an embodiment of the method of the invention.

As explained above, each actuator is associated with a map MAX (block 700) for its maximum allowed closed positions MAXWG,MAXHPT,MAXVGT, a map MIN (block 720) for its minimum allowed open positions MINWG,MINHPT,MINVGT and map FeedForward (block 710) for its feedforward positions values FFWDWG,FFWDHPT,FFWDVGT.

With the values in these map, a range of values representing positions of the actuators can be calculated and each range can associated to a corresponding range of the control variable PID (block 750).

Then a value of a parameter representative of a pressure in the intake manifold 200 is determined by the pressure sensor 350 or by other means such as a mathematical model and if the determined pressure value is lower than the desired value thereof, a pressure build up sequence is selected. If the determined pressure value is higher than the desired value thereof, a pressure discharge sequence is selected.

Finally a value of the two-stage turbocharger 500 system control variable PID is determined as a function of the difference between the determined value of the parameter and a desired value thereof (block 730).

On the basis of this PID value, which may fall in any of the ranges defined with reference to figures 6-9, the corresponding actuator to be actuated is determined (block 760) and the PlO value is added (block 740) to the FFWD position value for that actuator in order to start its actuation (block 770). while the non selected actuators are not actuated.

The procedure may be continued until the desired pressure value in the intake manifold is reached and, if the selected actuator reaches its MAX or MIN position, switching to the next actuator in the pressure build up or discharge sequence previously determined.

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

automotive system internal combustion engine (ICE) engine block 125 cylinder cylinder head camshaft piston crankshaft 150 combustion chamber cam phaser fuel injector intake manifold 205 intake line 207 high-pressure intake line 210 intake airport 215 valves of the cylinder 220 exhaust gas port 225 exhaust manifold 230 turbocharger 240 compressor 244 exhaust line portion 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 exhaust aftertreatment device 285 SCR catalyst 290 VGT actuator 300 EGR system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure sensor 445 accelerator pedal position sensor 450 electronic control unit (ECU) 460 data carrier 500 turbocharger system 505 high-pressure turbocharger 507 low-pressure turbocharger 510 HPT bypass 520 wastegate 540 compressor of low-pressure turbocharger 550 turbine of low-pressure turbocharger 590 high-pressure compressor bypass device 600 block 610 block 620 block 630 block 640 block 650 block 700 block 710 block 720 block 730 block 740 block 750 block 760 block 770 block

Claims

CLAIMS1. A method of controlling a two-stage turbocharger system (500) of an internal combustion engine (110) comprising a plurality of regulating devices (290,510,520) for varying a flow of engine exhaust gas in the two-stage turbocharger (500) system, the method complising the steps of: -determining a value of a parameter representative of a pressure in an intake manifold (200), -determining a target value of the parameter on the basis of an engine operating point, -determining a value of a control variable (PlO) for the two-stage turbocharger (500) as a function of the difference between the determined value of the parameter and the target value thereof, -selecting one of the regulating devices (290,510,520) on the basis of the determined value of the control variable (PlO), -actuating the selected regulating device.
2. A method according to claim 1 wherein the regulating device (290,510,520) is selected using a map correlating each of the regulating devices with a corresponding range of values of the control variable (PID).
3. A method according to claim 1, comprising a step of increasing pressure in the intake manifold (200) if the determined value of the parameter is lower than the target value thereof, the pressure increase being generated by actuating the selected regulating device until it reaches a maximum allowed closed position (MAX0, MAXHPTIMAXVGT).
4. A method according to claim 3, wherein if the selected regulating device reaches the maximum allowed closed position when the determined value of the parameter is still lower than the target value, the intake manifold pressure increase is continued by actuating the other regulating devices one at a time according to a predetermined sequence.
5. A method according to claim 1, comprising a step of decreasing pressure in the intake manifold (200) if the determined value of the parameter is higher than the target value thereof, the pressure decrease being generated by actuating the selected regulating device until it reaches a minimum allowed open position MINWG,MINHPT,MINVGT).
6. A method according to claim 5, wherein if the selected regulating device reaches the minimum allowed open position when the determined value of the parameter is still higher than the target value, the intake manifold pressure decrease is continued by actuating the other regulating devices one at the time according to a predetermined sequence.
7. A method according to claim 1, wherein the regulating devices include a wastegate valve (520) of a turbine (550) of the second turbocharger (507).
8. A method according to claim 1, wherein the regulating devices include a pressure turbine bypass valve (510) of a turbine (240) of the first turbocharger (505).
9. A method according to claim 1 wherein the regulating devices include a variable geometry turbine (290) of the first turbocharger (505).
10. An internal combustion engine (110) equipped with a two-stage turbocharger system (500) comprising a plurality of regulating devices (290510,520) for varying a flow of engine exhaust gas in the two-stage turbocharger (500) system1 the engine (110) being managed by an Electronic Control Unit (450) configured for carrying out the method according to any of the preceding claims.
11. A computer program comprising a computer code suitable for performing the method according to any of the preceding claims.
12. A computer program product on which the computer program of claim 11 is stored.
13. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 11.