GB2530203A

GB2530203A - A method of detecting a catalyst of a selective catalytic reduction system

Info

Publication number: GB2530203A
Application number: GB1521852.2A
Authority: GB
Inventors: Roberto Argolini; Alberto Giordano
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2015-12-10
Filing date: 2015-12-10
Publication date: 2016-03-16
Also published as: GB201521852D0

Abstract

The method detects the absence of a catalyst 281 of a selective catalytic reduction (SCR) system 280 of an internal combustion engine 110, preferably of a diesel powered motor vehicle 100. The catalyst is located in an exhaust pipe 275 of the engine and the method comprises the steps of: determining a value of a parameter indicative of a flow resistance of exhaust gas through the catalyst; and identifying an absence of the catalyst if the determined value is lower than a reference value when compared (805, figure 3). Ideally the value is a mean value (804, figure 3) calculated from a plurality of values (803, figure 3) obtained over time. The values are preferably calculated based upon a formula that uses measurements of (i.) differential pressure of exhaust gas across the catalyst and (ii.) an exhaust gas volumetric flow rate through the catalyst in combination with a correction factor calculated as a function of a catalyst temperature. Preferably the value is only calculated when a differential pressure across the catalyst and a volumetric flow rate through the exhaust pipe are greater than respective predetermined values (801,802, figure 3).

Description

A METHOD OF DETECTING A CATALYST OF A SELECTIVE CATALYTIC REDUC-

TION SYSTEM

TECHNICAL FIELD

The present disclosure relates to a method of detecting a catalyst of a selective catalytic * 10 reduction (SCR) system of an internal combustion engine, in particular of an internal * combustion engine (e.g. gasoline engine or Diesel engine) of a motor vehicle.

BACKGROUND

It is known that modern internal combustion engines, in particular diesel engines, are equipped with a selective catalytic reduction (SCR) system designed to reduce the nitro- * gen oxides (NOr) emitted during the operation of the internal combustion engine. The SCR system comprises a catalyst, which is disposed in an exhaust pipe of the engine to convert the nitrogen oxides into diatonic nitrogen and water with the aid of a reducing agent. The reducing agent may be injected in liquid state into the exhaust pipe by a dedi- cated injector that is disposed upstream of the catalyst. The injector receives the reduc- ing agent from a tank by means of a pump which is in fluid communication with the injec-tor via a supply conduit.

Current European On Board Diagnostic (EOBD) legislation requires that a test of detect-ing an SCR catalyst is performed by an on Board diagnostic software of the vehicle for verifying the actual presence of a catalyst in the selective catalytic reduction (SCR) sys-tem.

This detecting test is required to avoid tampering situation wherein the catalyst is re-moved by the user.

In view of the above, it is an object of the present disclosure to provide a method of de- tecting a catalyst of a selective catalytic reduction system of an internal combustion en-gine.

This object is achieved by the embodiments of the invention having the features recited in the independent claims. The dependent claims delineate preferred and/or especially advantageous aspects of the various embodiments of the invention.

SUMMARY

An embodiment of the invention provides a method of detecting a catalyst of a selective catalytic reduction system of an internal combustion engine, wherein the catalyst is dis-posed in an exhaust pipe of the engine, and wherein the method comprises the steps of: -determining a value of a parameter indicative of a flow resistance of exhaust gas through the catalyst, and -identifying an absence of the catalyst if the value is lower than a reference value there-of.

As a matter of fact, the method allows to perform a diagnostic test for detecting the cata- lyst of a selective catalytic reduction system by means of a reliable and low cost proce-d ure.

According to an aspect of the method, the value of the parameter indicative of the flow resistance of exhaust gas through the catalyst is a mean value of a plurality of deter-mined values of the parameter indicative of the flow resistance.

Thanks to this aspect of the invention the identifying of an absence of the catalyst is more reliable and robust.

According to another aspect of the rnethod, the value of the parameter indicative of the flow resistance of exhaust gas through the catalyst is determined by means of the follow-ing formula: FlowRes = Jc[flT)] Ap

V

wherein k[f(70] is a correction factor calculated as a function of a catalyst temperature, Ap is a differential pressure value of the exhaust gas upstream and downstream of the catalyst, and is an exhaust gas volumetric flow rate through the catalyst.

This aspect provides a reliable and easy solution for determining the flow resistance of exhaust gas.

According to an aspect of the method, the step of determining a plurality of values of a flow resistance of exhaust gas through the catalyst is performed only if the following en-abling conditions are fulfilled: -a differential pressure value of the exhaust gas upstream and downstream of the catalyst is greater than a predetermined value, and -a volumetric flow rate of the exhaust gas flowing through the exhaust pipe is greater than a predetermined value.

This aspect provides reliable and robust enabling conditions of the diagnostic test for de-tecting the catalyst of the selective catalytic reduction system.

An embodiment of the invention provides for an internal combustion engine equipped with a selective catalytic reduction system comprising a catalyst, disposed in an exhaust pipe of the engine, and with an electronic control unit configured to: -determining a value of a parameter indicative of a flow resistance of exhaust gas through the catalyst, and -identifying an absence of the catalyst if the value is lower than a reference value there-of.

This embodiment provides the same advantages disclosed for the method above.

The present invention may be also embodied in the form of a computer program com-prising a computer-code for performing, when run on a computer, the method described above, or in the form of a computer program product comprising a carrier on which said computer program is stored. In particular, the present invention may be embodied in the form of a control apparatus for an internal combustion engine, comprising an electronic control unit, a data carrier associated to the electronic control unit and the computer pro-gram stored in the data carrier. Another embodiment may provide an electromagnetic signal modulated to carry a sequence of data bits which represent the computer pro-gram.

Another embodiment of the invention provides an apparatus for detecting a catalyst of a selective catalytic reduction system of an internal combustion engine, wherein the cata-lyst is disposed in an exhaust pipe of the engine, and wherein the apparatus comprises: -means for determining a value of a parameter indicative of a flow resistance of exhaust gas through the catalyst, and -means for identifying an absence of the catalyst if the value is lower than a reference value thereot This embodiment achieve basically the same effects of the method above, in particular that of detecting a catalyst of a selective catalytic reduction system.

According to another aspect of the apparatus the value of the parameter indicative of the flow resistance of exhaust gas through the catalyst is a mean value of a plurality of de-termined values of the parameter indicative of the flow resistance.

According to another aspect of the apparatus, the values of a flow resistance of exhaust gas through the catalyst is determined by means of the following formula: FlowRes = Ic[J1T)] -Ap

V

wherein k[f(7')] is a correction factor calculated as a function of a catalyst temperature, Ap is a differential pressure value of the exhaust gas upstream and downstream of the catalyst, and P is an exhaust gas volumetric flow rate through the catalyst.

This aspect provides a reliable and easy solution for detecting the catalyst of the selec-tive catalytic reduction system.

According to an aspect of the apparatus, the means for determining, in a predetermined time interval, a plurality of values of a flow resistance of exhaust gas through the catalyst is performed only if the following enabling conditions are fulfilled: -a differential pressure value of the exhaust gas upstream and downstream the catalyst is greater than a predetermined value, and -a volumetric flow rate of the exhaust gas flowing through the exhaust pipe is greater than a predetermined value.

This aspect the same advantages disclosed for the method above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention Will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 shows an automotive system.

Figure 2 is a cross-section of an internal combustion engine belonging to the automotive systemoffigurel.

Figure 3 is a flowchart of a method for detecting a catalyst of the 5CR system of figure 1.

DETAILED DESCRIPTION

Some embodiments may include a motor vehicle (e.g. a passenger car) that embodies an automotive system 100, as shown in figures 1 and 2. The automotive system 100 in-cludes 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, re-sulting 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 in-take port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail in fluid communication with a high pressure fuel pump 180 that increases the pres-sure of the fuel received from a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

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

An air intake duct 205 may provide air from the ambient environment to the intake mani-fold 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 tur-bocharger 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. This example shows a variable geometry turbine (VGT) with a VGT actuator 255 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodi-ments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust gases exit the turbine 250 and are directed into an exhaust system 270.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. In the present example, the aftertreatment devices include a selective catalytic reduction (SCR) system 280 that comprises an SCR catalyst 281 (also referred as SCR converter) which is disposed in the exhaust pipe 275 for converting the nitrogen oxides contained in the exhaust gas into diatonic nitrogen and water.

The selective catalytic reduction (SCR) system 280 comprises also a differential pies-sure sensor 282 which is connected to the exhaust pipe 275 downstream and upstream of the SCR catalyst 281 for measuring a differential pressure value of the exhaust gas flowing through the SCR catalyst 281.

The aftertreatnient devices may further include a lean NO traps (LNT) 289 disposed in the exhaust pipe 275, and a particulate filters 290 disposed in the exhaust piper 275 up-stream of the SCR catalyst 281 and downstream the lean NO traps (LNT) 289.

Other embodiments may further include an exhaust gas recirculation (EGR) system 300, as shown in figure 1, 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 and an EGR valve 320 to regulate 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, the DEF pressure sensor 286, a NOx sensor 291 disposed in the exhaust pipe 275 between the oxidation catalyst 289 and the SCR cata-lyst 281, a NOx sensor 292 disposed in the exhaust pipe 275 between the SCR catalyst 281 and the particulate filter 290, an exhaust gas temperature sensor 293 disposed in the exhaust pipe 275 between the oxidation catalyst 289 and the SCR catalyst 281, 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, 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 DEF injector 282, the heaters 287 and 288, the electric motor 294 of the DEF pump 284, the throttle body 330, the EGR Valve 320, the VGT actuator 255, and the cam phaser 155. Note, dashed lines are used to indicate communication be- tween the ECU 450 and the various sensors and devices, but some are omitted for clari-ty.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system 460 and an interface bus. 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 interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The memory system 460 may include various storage types includ-ing optical storage, magnetic storage, solid state storage, and other non-volatile memory.

The program stored in the memory system 460 is transmitted from outside via a cable or in a wireless fashion. Outside the automotive system 100, the program is normally visible as a computer program product, which is also called computer readable medium or ma-chine readable medium in the art, and which should be understood to be a computer program code residing on a carrier, said carrier being transitory or non-transitory in na-ture with the consequence that the computer program product can be regarded to be transitory or non-transitory in nature.

An example of a transitory computer program product is a signal, e.g. an electromagnetic signal such as an optical signal, which is a transitory carrier for the computer program code. Carrying such computer program code can be achieved by modulating the signal by a conventional modulation technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electro-magnetic signal. Such signals are e.g. made use of when transmitting computer program code in a wireless fashion via a WiFi connection to a laptop. In case of a non-transitory computer program product the computer program code is embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrieva-ble way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an Asic, a CD or the like.

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

The ECU 450 may be configured to perform a test for detecting the catalyst 281 of the selective catalytic reduction (8CR) system 280, thereby using a parameter indicative of the flow resistance of exhaust gas through the SCR catalyst 281.

According to an embodiment of the invention, specifically a flow resistance of exhaust gas through the 8CR catalyst 281 is chosen as the parameter indicative of the flow re-sistance of exhaust gas through the catalyst.

In detail, the ECU 450 determines, by means of the differential pressure sensor 282, a plurality of values FIowResz. ....FIowRes of the flow resistance of exhaust gas through the SCR catalyst 281 (blocks 803).

According to an embodiment of the invention each of the values of the flow resistance of exhaust gas through the SCR catalyst 281 is determined by means of the following for-mula: FlcwRes = k[f(T)] Ap

V

wherein k[f(T)] is a correction factor calculated as a function of catalyst temperature, ftp is a differential pressure value measured by the differential pressure sensor 282, and his an exhaust gas volumetric flow rate through the 8CR catalyst 281.

Then the ECU 450 calculates (black 804) the mean value PlowRetmnnof the determined plurality of values of the flow resistance of exhaust gas through the SCR catalyst 281, by means of the formula: )PlowRes1 Fl9wRes,,19 = wherein n is the number of the plurality of values FlowResj FJowRes of a flow re-sistance of exhaust gas through the 8CR catalyst 281.

The ECU 450 compares (block 805) the mean value Plo WRC&.mean with a reference value FiowRet2-g and identifies an absence of the catalyst if the mean value F!owRes_mean is lower than the reference value P10 WROS_,W (block 806). The absence of the 5CR catalyst 281 is reported by activating a proper diagnostic trouble code.

On the contrary if the mean value FIowRes_ is equal or greater than the reference value FlowRes_mr (block 807) the SCR catalyst 281 is detected.

According to an aspect of this embodiment of the invention the ECU 450 determines a plurality of values FlowRes,, ....FIowRes, of a flow resistance of exhaust gas through the SCR catalyst 281, only after having checked that enabling conditions are fulfilled (block 801,802).

In detail, the ECU 450 measures (block 801) a differential pressure upstream and down-stream the SCR catalyst 281, by means of the differential pressure sensor 282, and a volumetric flow rate of an exhaust gas flowing through the exhaust pipe 275.

Then, the ECU 450 checks (block 802) that the measured differential pressure upstream and downstream the 5CR catalyst 281 is greater than a predetermined value, and that the measured volumetric flow rate of an exhaust gas flowing through the exhaust pipe 275 is greater than a predetermined value.

If both the two checks yield positive (i.e. the measured differential pressure is greater than the predetermined value and the measured volumetric flow rate is greater than the predetermined value), the ECU 450 performs the test for detecting the 5CR catalyst 281, else the test is not performed.

Both the predetermined values are experimentally determined during calibration test.The above disclosed method may be also actuated by the ECU 450 determining, by means of the sensor 282, a single value FJowRe&, of a flow resistance of exhaust gas through the catalyst 281.

In this case, the ECU 450 compares the single determined value FlowRes_i of the flow resistance of exhaust gas with the reference value FiowResf for identifying an absence of the 5CR catalyst 281. In detail, the absence of the 5CR catalyst 281 is identified if the value Plo wReg / is lower than the reference value FlowRes,.0,.

A different embodiment of the invention provides that, instead of the flow resistance, the differential pressure upstream and downstream the catalyst is directly used as the pa-rameter indicative of the flow resistance of exhaust gas through the SCR catalyst.

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 embodiment1 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.

REFERENCES

automotive system internal combustion engine engine block cylinder 130 cylinder head camshaft piston crankshaft combustion chamber 155 cam phaser fuel injector fuel rail fuelpump fuelsource 200 intake manifold 205 air intake duct 210 intake port 215 valves 220 exhaust port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 255 VGT actuator 260 intercooler 270 exhaust system 275 exhaust pipe 280 SCR system 281 5CR catalyst 282 differential pressure sensor 289 lean NO traps 290 particulate filter 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 and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 440 EGR temperature sensor 445 accelerator pedal position sensor 450 ECU 460 memory system 801 block 802 block 803 block 804 block 805 block 506 block 807 block 808 block