GB2500923A

GB2500923A - Method of increasing the efficiency of a lean NOx trap device of in a hybrid powertrain

Info

Publication number: GB2500923A
Application number: GB1206145.3A
Authority: GB
Inventors: Roberto Argolini; Tommaso De Fazio
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-04-05
Filing date: 2012-04-05
Publication date: 2013-10-09
Also published as: GB201206145D0

Abstract

A method for increasing the efficiency of the regeneration of a lean NOx trap (LNT) (281, fig.2) device of a hybrid powertrain 100 by interaction of the control strategies of the LNT and the hybrid power-train, comprising a motor-generator electric unit (MGU) 500, an internal combustion engine 110 with an exhaust system (270, fig.2), a lean NOx trap device, and an electronic control unit 450 to operate the method, the method comprising the following steps: comparing the exhaust gas temperature with a first predetermined threshold (TH2, fig.4) and with a second predetermined threshold (TH3, fig.4) and if the gas temperature is lower than said first threshold or higher than said second threshold actuating a hybrid optimisation strategy (HOS) manager. If the gas temperature is lower than the first threshold temperature the HOS manager will actuate the MGU as an electric generator and if the gas temperature is higher than the second threshold temperature the HOS manager will actuate the MGU as an electric motor.

Description

METHOD OF INCREASING THE EFFICIENCY OF A LEAN NOX TRAP DEVICE IN A

HYBRID P0 WER TRAIN

TECHNICAL FIELD

The present disclosure relates to a method of increasing the efficiency of a Lean NOx Trap device in a hybrid powertrain. More particularly, the invention relates to the regeneration phase of the LNT and provides a method to increase the efficiency of the conversion of NOx in nitrogen and ammonia.

BACKGROUND

It is known that any motor vehicle is equipped with a powertrain, namely with a group of components and/or devices that are provided for generating mechanical power and for delivering it to the final drive of the motor vehicle, such as for example the drive wheels of a car 23 A hybrid powertrain particularly comprises an internal combustion engine (ICE), such as for example a compression-ignition engine (Diesel engine) or a spark-ignition engine (gasoline or gas engine), and a motor-generator electric unit (MGU). The MGU can operate as an electric motor for assisting or replacing the ICE in propelling the motor vehicle, and can also operate as an electric generator, especially when the motor vehicle is braking, for charging an electrical energy storage device (battery) connected thereto.

Besides, the battery is provided for powering the MGU when it operates as electric motor, so that the only source of energy necessary for operating the hybrid powertrain is the ICE fuel.

The hybrid powertrain is controlled by an electronic control system according to a dedicated hybrid control strategy. During the traction of the motor vehicle, the hybrid control strategy provides for determining an overall value of mechanical power to be delivered to the wheels of the motor vehicle1 for splitting this overall value in a first contributing value of mechanical power to be requested to the ICE and a second contributing value of mechanical power to be requested to the MGU, and then far operating the ICE and the MGU to deliver to the wheels of the motor vehicle the respective contributing value of mechanical power.

In greater details, the splitting of the above mentioned overall power value is conventionally optimized by determining, among the infinite couples of first and second contributing power values whose addition is equal to the overall power value, the couple that minimize the a predetermined polynomial function, usually referred as target function, which quantifies an overall power that is lost due to the operation of the hybrid powertrain, namely a quantity of power that has been supplied to the hybrid powertrain through the ICE fuel, but that has not been delivered to the final drive of the motor vehicle, for example because it has been dissipated due to specific aspect of the hybrid powertrain operation.

As a consequence of this optimization, the first contributing power value is always positive, whereas the second contributing power value may be either positive or negative. If the second contributing power value is positive, the MGU is operated as an electric motor that actually supplies mechanical power to the final drive If the second contributing power value is negative, the MGU is operated as an electric generator that actually absorbs mechanical power from the final drive.

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 [NT 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 (NOr) 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 (NOX) from the LNT.

The [NT are operated cyclically, for example by switching the engine from lean-burn 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.

As can be seen from Figure 4, the regeneration efficiency is strongly influenced by exhaust gas temperature. During low load conditions and when the engine is still not warmed up can be very difficult to perform an efficient regeneration. In the low temperature area, left part of the graph, T c TH2I the system is very inefficient and the regeneration can lead to a significant NOX slip due to the fact that the conversion efficiency is really low. On the other side, the efficiency also decreases if the exhaust gas temperature is very high (1> TH3), above all in case of aged catalyst.

Therefore a need exists for a method that allows to increase the efficiency during the regeneration phase of the LNT, allowing the exhaust gas temperature always lying in the optimal range (TH2 c I c Tl-13). More particularly, by operating the MGU as an electric generator it would be possible to get torque from the ICE, thus increasing the ICE torque and, consequently, the gas temperature, white by operating the MGU as an electric motor it would be possible to provide torque to the ICE, therefore reducing the ICE torque and, consequently, the exhaust gas temperature.

An object of an embodiment of the invention is to provide a method for increasing the efficiency of a Lean NOx Trap device in a hybrid powertrain, during its regeneration phase.

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 especially advantageous aspects.

SUMMARY

An embodiment of the invention provides a method of increasing the efficiency of the regeneration of a lean NOx trap device of a hybrid powertrain, comprising a motor-generator electric unit, an internal combustion engine with an exhaust system and at least a lean NOx trap device, and an electronic control unit to operate the method, the method comprising the following steps: -comparing the exhaust gas temperature with a first predetermined threshold (TH2) and with a second predetermined threshold (TH3) and, if the gas temperature is lower than said first threshold (TH2) or higher than said second threshold (TH3), -actuating a HOS manager.

Consequently, an apparatus is disclosed for increasing the efficiency of the regeneration of a lean NOx trap device of a hybrid powertrain, the apparatus comprising: -means for comparing the exhaust gas temperature with a first predetermined threshold (TH2) and with a second predetermined threshold (TH3) and, if the gas temperature is lower than said first threshold (TH2) or higher than said second threshold (TH3), -means for actuating a HOS manager.

An advantage of this embodiment is that it allows to increase the efficiency of the NOx conversion during regeneration, avoiding the effect of the temperature on the NOX conversion rate.

According to another embodiment of the invention, if the gas temperature is lower than said first threshold (TH2), the HOS manager will actuate the MGU as electric generator, thus increasing the torque provided by the ICE.

An advantage of this embodiment is that the electric generator will charge the battery not only during cut-off periods but also before the LNT regeneration phase.

According to a further embodiment of the invention, if the gas temperature is higher than said second threshold (TH3), the HOS manager will actuate the MGU as electric motor, thus decreasing the torque provided by the ICE An advantage of this embodiment is to increase the LNT regeneration efficiency.

According to a still further embodiment, the release manager of the LNT regeneration is able to allow the start of the regeneration process if some conditions like engine working conditions, temperature, pressure, air control and air/fuel ratio are satisfied.

According to another embodiment, the NOx storage model is based at least on the following parameters: temperature, flowrate, catalyst aging and sulphur amount.

According to a still further embodiment, the hybrid powertrain comprises a motor-generator electric unit, an internal combustion engine and an electronic control unit, which is configured for carrying out the method according to the inventions.

An advantage of this embodiment is that it allows to reduce the system complexity of a hybrid powertrain and to pursuit integration.

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 rnethod 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 schematically represents a hybrid powertrain of a motor vehicle.

Figure 2 shows in more details an internal combustion engine belonging to the hybrid powertrain of figure 1.

Figure 3 is a section A-A of the internal combustion engine of figure 2.

Figure 4 is a graph depicting the behavior of the catalyst efficiency vs. exhaust gas temperature.

Figure 5 is a flowchart of a method for increasing the efficiency of the LNT, according to the invention Figure 6 is a graph depicting the behavior, among others, of the required torque and the exhaust gas temperature.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include a motor vehicle's mild hybrid powertrain 100, as shown in Figures 1, that comprises an internal combustion engine (ICE) 110, in this example a diesel engine, a motor-generator electric unit (MGU) 500, an electric energy storage device (battery) 600 electrically connected to the MGU 500, and an electronic control unit (ECU) 450 in communication with a memory system 460.

As shown in Figures 2 and 3, the ICE 110 has an engine black 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 ignited1 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) 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 (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. 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 MGU 500 is an electric machine, namely an electro-mechanical energy converter, which is able either to convert electricity supplied by the battery 600 into mechanical power (i.e., to operate as an electric motor) or to convert mechanical power into electricity that charges the battery 600 (i.e., to operate as electric generator). In greater details, the MGU 500 may comprise a rotor, which is arranged to rotate with respect to a stator, in order to generate or respectively receive the mechanical power. The rotor may comprise means to generate a magnetic field and the stator may comprise electric windings connected to the battery 600, or vice versa. When the MGU 500 operates as electric motor, the battery 600 supplies electric currents in the electric windings, which interact with the magnetic field to set the rotor in rotation. Conversely, when the MGU 500 operates as electric generator, the rotation of the rotor causes a relative movement of the electric wiring in the magnetic field, which generates electrical currents in the electric windings. The MGU 500 may be of any known type, for example a permanent magnet machine, a brushed machine or an induction machine. The MGU 500 may also be either an asynchronous machine or a synchronous machine.

The rotor of the MGU 500 may comprise a coaxial shaft 505, which is mechanically is connected with other components of the hybrid powertrain 100, so as to be able to deliver or receive mechanical power to and from the final drive of the motor vehicle. In this way, operating as an electric motor, the MGU 500 can assist or replace the ICE 110 in propelling the motor vehicle, whereas operating as an electric generator, especially when the motor vehicle is braking, the MGU 500 can charge the battery 600. In the present example, the MGU shaft 505 is connected with the ICE crankshaft 145 through a transmission belt 510, similarly to a conventional alternator starter. In order to switch between the motor operating mode and the generator operating mode, the MGU 500 may be equipped with an appropriate internal control system.

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 memory system 460. 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 and the MGU 500.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with the memory system 460 and an interface bus. The memory system 460 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 CPU is configured to execute instructions stored as a program in the memory system 460, and send and receive signals to/from the interface bus. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110 and the MGU 500.

In order to carry out these methods, the ECU 450 is in communication with one or more sensors and/or devices associated with the ICE 110, the MGU 500 and the battery 600.

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 MGU 500 and the battery 600. 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 temperature sensor 385, oil temperature sensor 385, a fuel rail pressure sensor 400, a camshaft position sensor 410, a crankshaft position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, a sensor 445 of a position of an accelerator pedal 446, and a measuring circuit 605 capable of sensing the state of charge of the battery 600.

Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110 and the MGU 500, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, the cam phaser 155, and the above mentioned internal control system of the MGU 500. 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 back to exhaust system 270, the proposed invention relies on the optimization of then regeneration phase of a LNT 281.

The LNT reduces engine-out exhaust gas constituents (CO and HC) with high efficiency and stores NOx during lean operating conditions. During rich operating conditions, the regeneration phase, the NOx are released and converted.

Experimental activities on the actual LNT technology show (Figure 4): > the LNT storage and conversion efficiency is strongly affected by the exhaust gas temperature > In the low temperature area, left part of the graph (T cTH2), the system is very inefficient and the regeneration can lead to a significant NOX slip due to the fact that the conversion efficiency is really low.

> The system also loses efficiency in the right part of the graph (T>TH3) The basic idea of the method is to increase the efficiency of the regeneration phase of the LNT, by let interacting the control strategies of the hybrid Powertrain -Hybrid Optimization Strategy manager which manages the torque provided or received by the electric motor-generator -together with the control strategies of the LNT, such as the NOx storage model, which predict the filling of the LNT and is based on temperature, flowrate, catalyst aging, sulphur amount, and the working conditions which allow a release manager of the LNT regeneration to start and let complete the regeneration process. Turning to Figure 5, a scheme illustrating the method is shown. The propaedeutic steps of the method are the followings: -detecting 20 when the NOx storage model has reached a predetermined threshold TH1, -detecting 21 if the release manager of the LNT regeneration is able to allow the start of the regeneration process according to the operating conditions (engine working conditions, temperature, pressure, air control and air/fuel ratio) These conditions let the regeneration process to start. The efficiency of such process is increased by the present invention, by actuating these further steps: -comparing 22 the exhaust gas temperature with a first predetermined threshold TH2 and with a second predetermined threshold TH3 if the gas temperature is lower than said first threshold TH2 or higher than said second threshold TH3 -actuating 23 the HOS manager.

According to the fact that the gas temperature is lower than said first threshold TH2, the HOS manager will actuate the MGU 500 as electric generator 24, thus increasing the torque provided by the ICE 100. On the other side, if the gas temperature is higher than said second threshold TH3, the HOS manager will actuate the MGU 500 as electric motor 25, thus decreasing the torque provided by the ICE 100.

Therefore the present invention is mainly based on the idea to synchronize the time spent to charge the battery by the Hybrid Optimization Strategy Manager with a LNT regeneration. In this way the increase of load due to the requested negative electric torque will naturally increase the exhaust gas temperature allow for a more efficient regeneration without extra energy consumption and improving the catalyst performances.

The graph in Fig. 6 illustrates the idea in a generic engine working condition (1500 rpm x 2 bar PME), with the electric machine working as generator In the graph, starting from a situation with no electric torque required by HOS, different values of electric torque have been requested ELi, EL2, EL3; consequently the combustion torque values CT1, CT2, CT3 increase according to the required electric torque; the third family of curves illustrate the different state of charge of the battery SOC1, SOC2, SOC3; finally, lower part, the resulting exhaust temperatures increase Ti, T2, T3 have also been measured.

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 hybrid powertrain internal combustion engine 120 engine block cylinder cylinder head camshaft piston 145 crankshaft combustion chamber cam phàser fuel injector fuel rail 180 fuel pump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 exhaust port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 DOC 281 LNT 282 DPF 290 VGT actuator 300 exhaust gas recirculation system 305 EGR conduit 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 in-cylinder pressure sensor 380 coolant temperature sensor 385 oil temperature sensor 400 fuel rail pressure sensor 410 camshaft position sensor 420 crankshaft position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator pedal position sensor 446 accelerator pedal 450 ECU 460 memory system 500 motor-generator electric unit 505 MGU shaft 510 transmission belt 600 battery 605 measuring circuit ELi, EL2, EL3 electric torque curves Cli, C12, CT3 combustion torque curves SOd, SOC2, SOC3 battery state of charge curves 11, 12, T3 exhaust temperature curves

Claims

CLAIMS1. Method of increasing the efficiency of the regeneration of a lean NOx trap (281) device of a hybrid powertrain (100), comprising a motor-generator electric unit (500), an internal combustion engine (110) with an exhaust system (270) having at least a lean NOx trap device (281)' the method comprising the following steps: -comparing (22) the exhaust gas temperature with a first predetermined threshold (TH2) and with a second predetermined threshold (TH3) if the gas temperature is lower than said first threshold (TH2) or higher than said second threshold (TH3) -actuating (23) a I-lOS manager.
2. Method according to claim 1, wherein if the gas temperature is lower than said first threshold (*12), the I-lOS manager will actuate the MGU (500) as electric generator (24), thus increasing the torque provided by the ICE (100).
3. Method according to claim 1, wherein if the gas temperature is higher than said second threshold (TH3), the HOS manager will actuate the MGU (500) as electric motor (25), thus decreasing the torque provided by the ICE (100).
4. Method according to claim 1, wherein release manager of the LNT regeneration is able to allow the start of the regeneration process if some conditions like engine working conditions, temperature, pressure, air control, air/fuel ratio, are satisfied.
5. Method according to claim 1, wherein said NOx storage model is based at least on the following parameters: temperature, flowrate, catalyst aging, sulphur amount.
6. Hybrid powertrain (100), comprising a motor-generator electric unit (500), an internal combustion engine (110), an electronic control unit (450) configured for carrying out the method according to claims 1-5.
7. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-5.
8. Computer program product on which the computer program according to claim 7 is stored.
9. 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 7 stored in a memory system (460).
10. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 7.