GB2502368A

GB2502368A - Controlling an Internal Combustion Engine Fitted with a Variable Geometry Turbine

Info

Publication number: GB2502368A
Application number: GB1209337.3A
Authority: GB
Inventors: Martin Miertschink; Andreas Rauscher
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-05-25
Filing date: 2012-05-25
Publication date: 2013-11-27
Anticipated expiration: 2032-05-25
Also published as: GB201209337D0; GB2502368B

Abstract

The invention provides a method of controlling an internal combustion engine of an automotive system, the engine comprising a Variable Geometry Turbine (VGT) (250, fig.1) and a Variable Geometry Turbine actuator (290, fig.1), the method, being applicable during engine transient phases and with satisfied enabling criteria 20, comprising opening 21 the Variable Geometry Turbine (250) up to a calibrated value, closing 22 the Variable Geometry Turbine (250) up to a feed forward value coming from the Variable Geometry Turbine actuator (290) closed loop pressure control, and cyclically repeating the above steps up to the end of the engine transient phase. Oscillating the vanes of a VGT during an engine transient phase will improve turbine throttling effects and reduce the damping of pulsating exhaust gases and the engines pumping losses.

Description

METHOD OF CONTROLLING AN INTERNAL COMBUSTION ENGINE

TECUNICAL FIELD

The present disclosure relates to a method of controlling an internal combustion engine, particularly for engines provided with a turbocharger having a Variable Geometry Turbine (VGT).

BACKGROUND

As known, modem internal combustion engines, particularly high speed Diesel engines, are more and more requiring the so called "low end torque", which can be achieved by improving the engine transient behavior. For turbocharged engines, this requires the capability of fast boost pressure build up, which in turn can be achieved by fast spin up of turbocharger.

Several technologies for turbocharger fast spin up are already known in the technique.

For example, the turbocharger can be realized with a low mass moment of inertia1 in other words, lightweight turbine and compressor rotors and shaft. Alternatively, small turbochargers can be realized in respect to expected engine power. Finally, and especially for diesel engines, Variable Geometry Turbine can be adopted, in order to get a bigger range with high torque.

In the latter case, the use of a VGT provides advantages in fast pressure build up, since when the vanes of the turbine housing are closed, a low cross-sectional area is available for inflowing gases, which in turn leads to a higher speed of flow and turbine wheel and, consequently, results in higher boost pressure.

Notwithstanding the above advantage, the use of the VGT, with the actual control strategies, leads to several drawbacks: vanes in closing position create a higher S backpressure of the exhaust gases and this results in higher pumping losses.

Furthermore, this also creates a damping of pulsating exhaust gases.

Therefore a need exists for a method of controlling the internal combustion engine, particularly its Variable Geometry Turbine, which provides at the same time a VGT fast closing combined with oscillating vanes to improve the engine transient behavior. By alternatively open and close the vanes would be possible to reduce the turbine throttle effects and consequently reduce the damping of pulsating exhaust gases and the engine pumping losses.

An object of this invention is to provide a method which manages the engine transient behavior, by controlling with a new strategy the Variable Geometry Turbine.

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, and by an electromagnetic signal having the features recited in the independent claims.

The dependent claims delineate preferred and/or especiallyadvantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of controlling an internal combustion engine of an automotive system, the engine comprising a Variable Geometry Turbine and a Variable Geometry Turbine actuator, the method, being applicable during engine transient phases and with satisfied enabling criteria, comprising: -opening the Variable Geometry Turbine up to a calibrated value, -closing the Variable Geometry Turbine up to a feed forward value coming from the Variable Geometry Turbine actuator closed loop pressure control, -cyclically repeating the above steps up to the end of the engine transient phase.

Consequently, an apparatus is disclosed for controlling an intemal combustion engine of an automotive system, the apparatus comprising: -means for opening the Variable Geometry Turbine up to a calibrated value, -means for closing the Variable Geometry Turbine up to a feed forward value coming from the Variable Geometry Turbine actuator closed loop pressure control, -means for cyclically repeating the above steps up to the end of the engine transient phase.

An advantage of this embodiment is that it provides a method which optimizes the engine transient behavior and the fuel consumption during full load acceleration.

Furthermore, the method requires no hardware changes and can be easily integrated in actual engine control methods.

According to another embodiment of the invention, said Variable Geometry Turbine remains in open position for a time interval to, which is mapped as function of the engine speed.

An advantage of this embodiment is that the method is easy to be calibrated, since the frequency depends on current engine speed.

According to a further embodiment of the invention said Variable Geometry Turbine remains in closed position for a time interval t.

Also according to this embodiment, this method is easy to be calibrated since, the VGT position depends on closed loop pressure control output.

According to a still further embodiment, the enabling criteria, for this method to be applied, comprising: an engine transient request, an engine speed in the range 1100- 1800 rpm, an engaged gear in between from 4th to 6th an error between a desired boost pressure and an actual boost pressure greater than a calibrated threshold and a duty cycle of the VGT actuator inside its own safety margins.

These enabling criteria are preferred conditions for the method to be applied, since they guarantee the maximum efficiency of the strategy, without penalizing engine safety conditions.

According to another embodiment, the invention provides an internal combustion engine of an automotive system, the engine comprising a Variable Geometry Turbine and a Variable Geometry Turbine actuator, the automotive system being configured for carrying out the above method.

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 section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is a graph comparing the behavior of the VGT actuation by using a known method or the method according to the invention.

Figure 4 is a flowchart of a method of controlling the VGT actuation, according to an embodiment of the invention.

Figure 5 is a graph depicting the results of experimental tests, obtained by implementation of the new strategy.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 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 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 variable geometry turbine (VGT) 250 with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

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 (5CR) systems, particulate filters (DPF) or a combination of the last two devices, i.e. selective catalytic reduction system comprising a particulate filter (SCRF). Some 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 and 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 VOT 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 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 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 method according to the invention is related to the control of the VGT 250, provided with a vacuum or electrical actuator 290.

Variable Geometry Turbines (VGT) are a family of turbochargers, usually designed to allow the effective aspect ratio of the turbo to be altered as the engine conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds. If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbocharges aspect ratio can be maintained at its optimum.

Because of this, VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. VGTs tend to be much more common on diesel engines as the lower exhaust temperatures mean they are less prone to failure.

The few early gasoline-engine VGTs required significant pre-charge cooling to extend the turbocharger life to reasonable levels, but advances in material technology has improved their resistance to the high temperatures of gasoline engine exhaust and they have started to appear increasingly.

Normally the VGT actuator 290 is controlled by the ECU 450 by means of duty cycle electric command. High duty cycle leads vanes to be moved in closing position, while low duty cycle means that vanes are moved towards opening position. As easily understandable, closed vanes mean a low cross-sectional area for inflowing gases and in turn, higher speed of flow, higher speed of turbine wheel and higher boost pressure.

On the contrary, opened vanes mean a larger cross-sectional area for inflowing gases, lower speed of flow, lower turbine speed and consequently slower boost pressure build up.

Therefore, in steady state, with low engine speed and low mass flow, the vanes are fully closed to increase the speed of exhaust flow over the turbine wheel, while with high engine speed and high mass flow, the vanes are fully opened to reduce the speed of the exhaust flow over the turbine wheel. During engine transient conditions, when a fast boost pressure build up is required, the actual strategy (see Figure 3, continuous line 500, and Figure 4) requires a Feed Forward control 25 (eventually a PID control can be added, depending on boost error) to get 26 the vanes fully closed at the beginning of the load step (normally the duty cycle is about 95%), thus increasing speed of turbine wheel and boost pressure. Of course, the smaller the error between desired and actual boost, the more the VGT is getting opened.

As already mentioned the use of the VGT, with the actual control strategies, leads to drawbacks in terms of higher backpressure of the exhaust gases and, consequently, higher engine pumping losses. Furthermore, this also creates a damping of pulsating exhaust gases.

Therefore, the approach for the new strategy according to the present invention, is to define a method of controlling the Variable Geometry Turbine, which provides at the same time a VGT fast closing, to accelerate the turbine wheel and build up boost pressure, combined with oscillating vanes to improve the engine transient behavior and keep the speed of the turbocharger. By alternatively open and close the vanes of the VGT (see Figure 3, dotted line 510), it would be possible to reduce the turbine throttle effects and consequently reduce the damping of pulsating exhaust gases and the engine pumping losses.

While in different situation the actual strategy will remain valid and applicable, the new strategy (Figure 4) will be actuated when some enabling conditions are satisfied 20. First of all, a positive transient request should be required. Then, to be the strategy more effective, the engine speed should be in the range 1200-1800 rpm, the engaged gear in between from 4th to 6 (of course these gears need a faster pressure build up, since the automotive runs slower due to the engine speed broadband) and the error between a desired boost and the actual boost should be greater than a calibrated threshold.

Furthermore the duty cycle of the VGT actuator 290 should not oscillate too much, remaining inside its own safety margins. Being satisfied the enabling conditions, the new method, up to the end of the engine transient phase, cyclically operates between: -opening 21 of the Variable Geometry Turbine 250 up to a calibrated value and then leaving the VGT in open position 23 for a time interval, which is mapped as function of the engine speed, -closing 22 the Variable Geometry Turbine 250 up to a feed forward value coming from the Variable Geometry Turbine actuator 290, and then leaving the VGT in closed position 24 for a time interval t0, which is mapped as function of the engine speed.

Clearly, the alternating position of the VGT leads to oscillating vanes. The frequency of the oscillation is determined as function of the engine speed. For example, with an engine speed of 1200 rpm there are 10 exhaust strokes per second per cylinder.

Advantageously, this controls strategy could use the exhaust strokes of 2 cylinders. This means there are 20 exhaust strokes per second. Moreover, first tests, looking at the response of the system, show that it makes more sense to use the strategy every 4th stroke. This results in 5 exhaust strokes per second, in other words, a 0.2s window to open and close the VGT is available.

This new method brings several advantages: first of all, it optimizes the engine transient behavior and fuel consumption during full load acceleration; moreover, it does not require hardware change, can be easily implemented in the actual control strategies and calibrated. Furthermore, it provides the possibility to extend the functionality related to exhaust pulsation, since the frequency and the VGT position can be optimized to use the pulsation on its maximum. Finally, it would provide a faster control with upcoming electrical actuator.

Preliminary tests demonstrates that the efficiency of the strategy is much more improved, by carefully calibrating the opening and closing time intervals t0 and t: longer opening times leads to better engine speed up. In fact, Figure 5 shows the diagram of the engine speed vs. the engine speed according to three different variants: original (without new strategy, curve 520), variant N. 4 with 0,05s opening time and 0,2s closing time (curve 530) and variant N. 5 with 0,3s opening time and 0,2s closing time (curve 540). The new strategy is applied (i.e. fluttering is active) when the engine speed ranges between 1100 and 1500 rpm. In the first engine speed sub-range (A: 1100-1200 rpm)1 the frequency of variant 4 is worse than the original, white the frequency of Var.5 has no impact on engine speed up. In the second engine speed sub-range (B: 1200-1400 rpm) the original (without new strategy) has an engine speed drop, while frequency of Var.5 leads to better engine speed up. Finally, in the third engine speed sub-range (C: 1400-1 500 rpm) the frequency of Var.4 has no further impact, while the frequency of Var.5 leads to bad engine speed up. As expected the new strategy, in general, leads to a reduction of pumping losses, better engine speed up and better fuel consumption. For instance, it has been possible to achieve 2000rpm in 10.9s instead of 1 1.3s and a a better fuel consumption of 2.67%.

White 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 block

21 block 22 block 23 block 24 block block 26 block data carrier 100 automotive system F internal combustion engine engine block cylinder cylinderhead 135 camshaft piston crankshaft combustion chamber cam phaser 160 fuel injector fuel rail fuel pump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 Variable geometry turbine (VGT) 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 290 VGT actuator 300 exhaust gas recirculation 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 temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor - 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGS temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 500 VGT position curve (without new method) 510 VGT position curve (with new method) 520, 530, 540 Gradient engine speed curves time interval (VGT opening time) time interval (VGT closing time)

Claims

CLAIMS1. Method of controlling an internal combustion engine (110) of an automotive system (100), the engine comprising a Variable Geometry Turbine (250) and a Variable Geometry Turbine actuator (290), the method, being applicable during engine transient phases and with satisfied enabling criteria (20), comprising: -opening (21) the Variable Geometry Turbine (250) up to a calibrated value, -closing (22) the Variable Geometry Turbine (250) up to a feed forward value coming from the Variable Geometry Turbine actuator (290) closed loop pressure control1 -cyclically repeating the above steps up to the end of the engine transient phase.
2. Method according to claim 1, wherein said Variable Geometry Turbine (250) remains in open position (23) for a time interval (t0), which is mapped as function of the engine speed.
3. Method according to claim 1 or 2, wherein said Variable Geometry Turbine (250) remains in closed position (24) for a time interval (ta).
4. Method according to one of the previous claim, wherein the enabling criteria (20) comprising: an engine transient request, an engine speed in the range 1110-1800 rpm, an engaged gear in between from 4 to 6th an error between a desired boost pressure and an actual boost pressure greater than a calibrated threshold and a duty cycle of the VGT actuator (290) inside its own safety margins.
5. Internal combustion engine (110) of an automotive system (100), the engine comprising a Variable Geometry Turbine (250) and a Variable Geometry Turbine actuator (290), the automotive system (100) being configured for carrying out the method according to claims 1-4.
6. A 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 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 computer program according to claim 6 stored in the data carrier (40),
9. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 6.