GB2502835A

GB2502835A - Method of controlling torque generation during rich combustion modes in an internal combustion engine

Info

Publication number: GB2502835A
Application number: GB1210308.1A
Authority: GB
Inventors: Luca Scavone; Alberto Corsiatto; Andrea Dutto; Roberto Argolini
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-06-06
Filing date: 2012-06-06
Publication date: 2013-12-11
Also published as: GB201210308D0

Abstract

Disclosed is a method of managing torque generation during rich combustion modes in an internal combustion engine 110 of an automotive system 100. The engine comprises a plurality of air actuators, such as a variable geometry turbine VGT 290, exhaust gas recirculation EGR valve 320 and intake air throttle 330, fuel actuators, such as fuel injectors 160 and an exhaust system 270 provided with at least an after-treatment device 280, the after-treatment device being a lean NOx trap LNT 281. The method comprises acquiring a raw torque request, defining a torque shaping request based on said raw torque request, managing the air actuators based on said torque shaping request, filtering the torque shaping request and controlling the timing of the fuel actuators based on the filtered torque. The method allows control of the air flowing in to an engine to be correlated with the demanded fuel injection amount during rich operating conditions necessary to regenerate the LNT in such a way that the torque can be effectively controlled and torque fluctuation can be avoided. Engine system and control software are also disclosed.

Description

TORQUE MANAGEMENT METHOD DURING RICH COMBUSTION MODE IN AN

INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of managing the torque during rich combustion mode in an internal combustion engine, particularly for engines provided with a Lean NOx Trap (LNT) aftertreatment system.

BACKGROUND

As known, the requested torque represents the load that has to be produced by the engine. The fuel and air actuators have to move to certain positions in order to combine the fluids and produce the desired load in the combustion chamber.

Taking as an example a Diesel combustion engine, the torque produced by the combustion uses a very high air/fuel ratio (AFR): this means that in the combustion chamber there is abundance of air and the produced torque can be assumed as proportional to the injected fuel. In general, the actuators of the engine (EGR, throttle valve, VGT actuators, injectors) are governed by set point values, which are mapped as a function of engine speed and load. The input of the maps are named speed pointer and load pointer. For example, in normal lean combustion, the air actuators (usually slower than the fuel actuators) are driven by a load pointer that corresponds to the raw torque request, coming from the accelerator pedal request in normal condition.

On the contrary, the fuel actuators, which are very fast and are the principal parameter influencing the final torque, are driven by a load pointer that corresponds a shaped torque request. Infact, for diesel engines, the delivered torque cannot be a step function because it will cause oscillations in the driveline, that can be felt by the driver. For this reason the final requested and delivered torque request must be filtered in a way to obtain the wanted shape, that will not cause any oscillation and drive-ability issues, It is also known that the exhaust gas after-treatment systems of a Diesel engine can be provided, among other devices, with a Lean NO Trap (LNT).

A Lean NO Trap (LNT) is provided for trapping nitrogen oxides NO contained in the exhaust gas and is located in the exhaust line.

A LNT is a catalytic device containing catalysts, such as Rhodium, Platinum and Palladium, and adsorbents, such as barium based elements, which provide active sites suitable for binding the nitrogen oxides (NOX) contained in the exhaust gas, in order to trap them within the device itself.

Lean NO Traps (LNT) are subjected to periodic regeneration processes, whereby such regeneration processes are generally provided to release and reduce the trapped nitrogen oxides (NOr) from the LNT.

The LNT are operated cyclically, for example by switching the engine from lean-burn r operation to operation whereby an excess amount of fuel is available, referred also as rich operation or regeneration phase-During normal operation of the engine, the NO are stored on a catalytic surface. When the engine is switched to rich operation, the NO stored on the adsorbent site react with the reductants in the exhaust gas and are desorbed and converted to nitrogen and ammonia, thereby regenerating the adsorbent site of the catalyst.

Therefore, [NT typical combustion modes require rich combustion (AFR < Stoichiometric AFR): in those conditions, the engine fipal torque depends on both involved fluid quantities, air and fuel.

The boundary conditions to define the type of load pointer of each actuator are the following; * The torque is a combination of both air and fuel quantities in the combustion chamber, therefore to guarantee that the torque is the desired one, both quantities should follow the desired torque path. This means that raw torque request can't be used for the air actuators.

* The air actuators have, as in lean combustion modes, a slow dynamic compared to the fuel actuators. This means that, in transient conditions, if both air and fuel use a shaped torque request, fuel actuators will move faster than air actuators, causing an AFR in the combustion chamber much higher/lower than the desired one, while as known it's very important to run to a fixed AER value, during LNT rich combustion mode.

Therefore a need exists for a method that can guarantee, above all in transient r conditions, a correct dynamic of the air and fuel systems, in order to have acceptable performances from th! point of view of drivability and combustion control.

An object of this invention is to provide a method which manages the requested and then delivered the torque during rich combustion mode in an internal combustion engine, particularly for engines provided with a Lean NOx Trap (LNT) aftertreatment system, which requires rich combustion modes for its regeneration.

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.

1 5 The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides a method of managing torque generation during rich combustion modes in an internal combustion engine of an automotive system (100), the engine comprising a plurality of air actuators and fuel actuators, the method comprising: -acquiring a raw torque request, -defining a torque shaping request based on said raw torque request, -managing said air actuators based on said torque shaping request, -filtering said torque shaping request -managing said fuel actuators based on said filtered torque.

Consequently, an apparatus is disclosed for managing torque generation during rich combustion modes in an internal combustion engine of an automotive system, the apparatus comprising: -means for acquiring a raw torque request, -means for defining a torque shaping request based on said raw torque request, -means for managing said air actuators based on said torque shaping request, -means for filtering said torque shaping request -means for managing said fuel actuators based on said filtered torque.

An advantage of this embodiment is that it provides a method of managing torque generation in rich combustion mode, allowing smoother transition phases and no impact on drive-ability performance of the vehicle.

According to another embodiment of the invention, said filtered torque is also used in defining an air/fuel ratio set point.

An advantage of this embodiment is that a better control of the air/fuel ratio set point avoids that the AFR reaches too low values, which can damage the AFR sensor itself.

According to a further embodiment of the invention, said engine also comprises an exhaust system provided with at least an after-treatment device, the after-treatment device being lean NOx trap and the method is applied during the regeneration phase of said lean NOx trap.

An advantage of this embodiment is that the method can perform a better air/fuel ratio control in open loop, especially during tip in and tip out phases, being such control mandatory for a successful regeneration phase of the lean NOx trap.

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 case1 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 schematic view of the after-treatment system according to the invention.

Figure 4 is a flowchart of a method of managing the requested and delivered torque in lean combustion mode of an internal combustion engine, according to a known method.

Figure 5 is a flowchart of a method of managing the requested and delivered torque in rich combustion mode of an internal combustion engine according to an embodiment of the invention.

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 iSO 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) 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

S

aftertreatment devices 260. 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 281, hydrocarbon adsorbers, selective catalytic reduction (SCR) 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 (see Fig.3) can be provided with LNT upstream and downstream air/fuel sensors 263, 284 and LNT upstream and downstream temperature sensors. 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 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, including1 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 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.

To illustrate the method according to the invention, some background information must be provided. The torque request represents the load which has to be produced by the engine. The related actuators (mainly, air and fuel actuators) have to move to certain positions in order to combine and produce the desired load in the combustion chamber.

The torque produced by the combustion, in a typical Diesel engine, uses a very high Air to Fuel Ratio (AFR), meaning that in the combustion chamber there is abundance of air and the produced torque can be assumed as proportional to the injected fuel. Normally, the actuators of the engine (EGR, turbo-compressor, injectors, etc.) are governed through set point values, that are mapped as a function of engine speed and load (the * 25 input of the maps are named speed pointer and load pointer).

For example, in normal lean combustion, the air actuators, which are usually relatively slow and have low influence on the final torque produced by the engine, are driven by a load pointer (the value that enters the map and decides which value/position is the target of the actuator) that corresponds to the raw torque request (i.e. the accelerator pedal request in normal condition). On the contrary, the fuel actuators, which are very fast and are the principal parameter influencing the final torque, are driven by a load pointer that corresponds to the shaped torque request, which differs from the raw torque request being mathematically smoothed. In fact, in diesel engine it's not possible to have a stepwise torque because it will cause oscillation in the driveline that can be felt by the driver. For this reason the final torque request (shaped torque request) will be filtered in a way to obtain the wanted shape that will not cause any oscillation and drive-ability issues.

The method according to the invention starts from the consideration that in normal lean combustion modes, air actuators are commanded using a load pointer coming from the raw accelerator torque request. This is mainly done to minimize the turbo lag, since the air actuators are slower than the fuel actuators. On the contrary, fuel actuators are commanded using a shaped torque that it's taking in account all adjustment needed for drive-ability and all the limitation (e.g. smoke limit torque curve) to prevent black smoke.

In fig. 4, a known method of managing the requested and delivered torque in lean combustion mode is shown. The requested raw torque is acquired 20 and then transformed 21 in a torque shaping request. The set point values of the air actuators are managed 22 by the raw torque request, which is converted 26 in fuel request, while the set point values of the fuel actuators are managed 24 by the shaped torque request, converted 26 in mapped fuel request, as well. 1].

The same strategy cannot be used in rich mode. In case of a low AFR, the engine torque depends on both air and fuel, and a correlation between them needs to be guarantee in order not to vary the AFR. Therefore, air torque load pointer has been moved to a shaped torque and a special load pointer has been created to minimize the AFR control for fuel actuators As mentioned above, for air actuators a shaped torque request has been chosen as a load pointer: this torque information corresponds to the shaping of the raw request, to guarantee no oscillation on the driveline. Using shaped" torque on slow actuators will imply slow torque increases and slow acceleration of the vehicle. Anyway, considering that the engine can run in rich combustion mode in a limited zone of the engine map, this performance loss cannot be felt by the driver. In fact, this choice has been tested in vehicles and little difference in acceleration has been seen in measurements, while the driven has not been able to perceive any difference. Moreover, in lean mode the torque produced by the engine is depending on fuel actuators, which are governed by the same shaped torque request. This means that no torque jumps are created during the transition lean to rich or rich to lean, improving the vehicle performance and the driver perceptions.

For the fuel actuators, a new torque information has been created, through the filtering of the air load pointer, namely the shaped torque request. This new torque information has been called "filtered" torque request. The target is to filter the air load pointer in order to take into account the slow reaction of the air system to an increase/decrease of torque request. The filtering is obtained through a low pass filter with a calibratable coefficient that is depending on engine speed and load, thus taking into consideration that in different engine operating points the air dynamics can differ as well. By using this method the driver cannot perceive any difference with the one in which bath air and fuel are governed by the shaped torque request. Moreover, since fuel actuators in rich mode are governed by the same load pointer responsible of the torque production in lean mode, the filtering action starts after the end of the transition. This approach gives a good drivability performance during testing activity. Furthermore, no impact in stationary conditions will arise, since the two load pointers for air and fuel are the same. Moreover, a better performance of AFR control can be achieved in transient conditions, since open loop values are aligned with the current measured air and therefore closed loop action can be smaller. Finally, a better control of the air/fuel ratio set point avoids that the AFR reaches too low values (e.g., under 0,8), which can damage the AFR sensor itself.

Fig. 5 shows as in rich combustion mode, air actuators are managed by a shaped torque request, while fuel actuators are managed by a filtered shaped torque request. Mare in detail, the method according to the invention, starting from the acquisition 20 of a raw torque request (accelerator pedal), defines 21 a torque shaping request based on said raw torque request. The air actuators 290, 320, 330 will be managed 22 based on said torque shaping request. As far as the actuators is concerned, a further filtered 23 torque shaping request will be provided for managing 24 said fuel actuators 160 and, consequently, defining 25 an air/fuel ratio set point.

Advantageously, wherein the internal combustion engine 110 also comprises an exhaust system 270 provided with a lean NOx trap 281 the above method can be applied during the regeneration phase of said lean NOx trap 281.

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 block

21 block 22 block 23 block 24 block block 26 block data carrier 100 automotive system internal combustion engine engine block cylinder cylinder head 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 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 281 lean NOx trap 283 LNT upstream air/fuel ratio sensor 284 LNT downstream air/fuel ratio sensor 285 LNT upstream temperature sensor 286 LNT downstream temperature sensor 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 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU

Claims

CLAIMS1. Method of managing torque generation during rich combustion modes in an internal combustion engine (110) of an automotive system (100), the engine comprising a plurality of air actuators (290, 320, 330) and fuel actuators (160) and an exhaust system (270) provided with at least an after-treatment device (280), the after-treatment device being a lean NOx trap (281), the method comprising: -acquiring (20) a raw torque request, -defining (21) a torque shaping request based on said raw torque request, -managing (22) said air actuators (290, 320, 330) based on said torque shaping request, -filtering (23) said torque shaping request, -managing (24) said fuel actuators (160) based on said filtered torque.
2. Method according to claim 1, wherein said filtered torque is also used in defining (25) an air/fuel ratio set point.
3. Method according to claim 1 or 2, wherein said engine (110) also comprises an exhaust system (270) provided with at least an after-treatment device (280), the after-treatment device being a lean NOx trap (281) and the method is applied during the regeneration phase of said lean NOx trap (281).
4. Internal combustion engine (110) of an automotive system (100) equipped with an exhaust system (270), comprising at least an after-treatment device (280), the after-treatment device being a lean NOx trap (281), the engine also comprising a plurality of air actuators (290, 320, 330) and fuel actuators (160), the automotive system (100) comprising an electronic control unit (450) configured for carrying out the method according to claims 1-3.
5. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-3.
6. Computer program product on which the computer program according to claim 5 is stored.
7. 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 5 stored in the data carrier (40).
8. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 5.