Method and a system for determining a flow resistance across a particulate filter

Abstract

A method of determining a flow resistance across a particulate filter located downstream of an internal combustion engine in an exhaust system. The method comprises measuring a first differential pressure across the particulate filter, measuring a second differential pressure downstream of the particulate filter, determining a pressure ratio of the first differential pressure and the second differential pressure, and from said pressure ratio, determining a flow resistance across the particulate filter. The second differential pressure is measured across a selective catalytic reduction system.

Claims

1. An electronic implemented method of determining a flow resistance across a particulate filter in an exhaust system, which particulate filter is located downstream of an internal combustion engine, the method comprising: measuring, via pressure sensing device, a first differential pressure across the particulate filter; measuring, via pressure sensing device, a second differential pressure downstream of the particulate filter across a selective catalytic reduction system; determining, via an electronic control unit, a pressure ratio of the first differential pressure and the second differential pressure; determining, via an electronic control unit, if a flow of exhaust gas through the exhaust system exceeds a predetermined threshold value; and when said threshold value is exceeded, determining, via an electronic control unit, from said pressure ratio, a flow resistance across the particulate filter.

2. The method according to claim 1, wherein the first differential pressure and the second differential pressure are measured simultaneously.

3. The method according to claim 2, wherein the first differential pressure and the second differential pressure are measured using a single pressure sensing device.

4. The method according to claim 1, wherein the second differential pressure is used in the step of determining if the flow of exhaust gas through the exhaust system exceeds a predetermined threshold value.

5. The method according to claim 1, wherein the determined flow resistance is tested against an error criterion, and, given that the error criterion is fulfilled, an error code is generated, via an electronic control unit.

6. The method according to claim 5, wherein the error criterion is fulfilled if the determined flow resistance exceeds a predetermined upper threshold value or falls below a predetermined lower threshold value.

7. A system for determining a flow resistance across a particulate filter in an exhaust system, which particulate filter is located downstream of an internal combustion engine, the system comprising: pressure sensing means for determining a first differential pressure across the particulate filter and a second differential pressure downstream of the particulate filter across a selective catalytic reduction system; processing means configured to determine a pressure ratio of the first differential pressure and the second differential pressure; processing means configured to determine if a flow of exhaust gas through the exhaust system exceeds a predetermined threshold value; and processing means configured to determine a flow resistance only when said predetermined threshold value is exceeded.

8. The system according to claim 7, wherein the pressure sensing means comprises a single pressure sensing device configured to measure the first differential pressure and the second differential pressure.

9. A computer program product comprising computer program code stored in a non-transitory computer-readable medium readable by a computer, said computer program product used for determining a flow resistance across a particulate filter in an exhaust system, which particulate filter is located downstream of an internal combustion engine, wherein said computer program code comprising computer instructions to cause one or more computer processors to perform the following operations: measuring a first differential pressure across the particulate filter; measuring a second differential pressure downstream of the particulate filter across a selective catalytic reduction system; determining a pressure ratio of the first differential pressure and the second differential pressure; determining if a flow of exhaust gas through the exhaust system exceeds a predetermined threshold value; and when said threshold value is exceeded, determining from said pressure ratio, a flow resistance across the particulate filter.

10. An electronic control unit of a motor vehicle comprising: an execution means; a memory connected to the execution means; a data storage medium which is connected to the execution means; and computer program product comprising computer program code stored in a non-transitory computer-readable medium readable by a computer, said computer program product used for determining a flow resistance across a particulate filter in an exhaust system, which particulate filter is located downstream of an internal combustion engine, wherein said computer program code comprising computer instructions to cause one or more computer processors to perform the following operations: measuring a first differential pressure across the particulate filter; measuring a second differential pressure downstream of the particulate filter across a selective catalytic reduction system; determining a pressure ratio of the first differential pressure and the second differential pressure; determining if a flow of exhaust gas through the exhaust system exceeds a predetermined threshold value; and when said threshold value is exceeded, determining from said pressure ratio, a flow resistance across the particulate filter.

11. A motor vehicle comprising an electronic control unit, wherein said electronic control unit comprises: an execution means; a memory connected to the execution means; a data storage medium which is connected to the execution means; and computer program product comprising computer program code stored in a non-transitory computer-readable medium readable by a computer, said computer program product used for determining a flow resistance across a particulate filter in an exhaust system, which particulate filter is located downstream of an internal combustion engine, wherein said computer program code comprising computer instructions to cause one or more computer processors to perform the following operations: measuring a first differential pressure across the particulate filter; measuring a second differential pressure downstream of the particulate filter across a selective catalytic reduction system; determining a pressure ratio of the first differential pressure and the second differential pressure; determining if a flow of exhaust gas through the exhaust system exceeds a predetermined threshold value; and when said threshold value is exceeded, determining from said pressure ratio, a flow resistance across the particulate filter.

12. A motor vehicle according to claim 11, wherein the motor vehicle is a truck or a bus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will in the following be further described by means of example with reference to the appended drawings, wherein

(2) FIG. 1 shows a schematic drawing of an exhaust system including a system according to an embodiment of the invention,

(3) FIG. 2 shows a flow chart of a method according to an embodiment of the invention, and

(4) FIG. 3 shows a schematic drawing of a control unit for implementing a method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) An exhaust system of an internal combustion engine 1 in a motor vehicle is schematically shown in FIG. 1. The exhaust system comprises a diesel oxidation catalyst unit 2, a particulate filter 3 located downstream of the oxidation catalyst unit 2, and further a selective catalytic reduction (SCR) system 4 downstream of the particulate filter 3. The exhaust system further comprises pressure sensing means in the form of a differential pressure sensor 5. The differential pressure sensor 5 is configured to simultaneously measure a first differential pressure P.sub.1 across the particulate filter 3 and a second differential pressure P.sub.2 across the SCR system 4. For this purpose, the pressure sensor 5 has pressure inlet ports 8, 9, 10 located upstream the particulate filter 3, between the particulate filter 3 and the SCR system 4, and downstream the SCR system 4, respectively. Processing means in the form of a processing unit 6 is connected to the differential pressure sensor 5. The processing unit 6 is configured to calculate a pressure ratio P.sub.1/P.sub.2 and, based on said pressure ratio, a flow resistance R across the particulate filter 3, which is related to the pressure ratio as R=k.Math.P.sub.1/P.sub.2, wherein k is a constant. During operation of the internal combustion engine 1, exhaust gases are generated and follow the direction of the arrows through exhaust system before being emitted through an exhaust pipe 7.

(6) The flow chart in FIG. 2 illustrates a method according to an embodiment of the invention. Using the differential pressure sensor 5, the first differential pressure P.sub.1 across the particulate filter 3 and the second differential pressure P.sub.2 across the SCR system 4 are measured simultaneously in a step S1. In a step S2, it is checked whether the volume flow of exhaust gas through the exhaust system exceeds a predetermined threshold value .sub.T. This determination is performed using the second differential pressure P.sub.2 across the SCR system 4, which is proportional to the flow . If it is determined that the flow exceeds the predetermined threshold value .sub.T, the pressure ratio P.sub.1/P.sub.2 is determined in a step S3 using the processing unit. From the pressure ratio P.sub.1/P.sub.2, the flow resistance R across the particulate filter 3 is calculated in a step S4.

(7) If the flow of exhaust gas is lower than the predetermined threshold value .sub.T, no determination of the pressure ratio P.sub.1/P.sub.2 is carried out until the flow exceeds the threshold value.

(8) Once the flow resistance R across the particulate filter 3 has been calculated, it may be tested against a preset error criterion in a step S5. Given that the error criterion is fulfilled, an error code is generated in a step S6. The error criterion may be set such that it is fulfilled if the determined flow resistance R exceeds a predetermined upper threshold value R.sub.U, indicating that the particulate filter 3 is clogged, or falls below a predetermined lower threshold value R.sub.L, indicating that there are e.g. cracks in the particulate filter 3. Different error codes are generated depending on the outcome of the testing against the error criterion. The error code may in case of a clogged particular filter 3 e.g. trigger a regeneration process, or in the case of a cracked filter trigger generation of an alarm signal, alerting a driver of a vehicle in which the exhaust system is located that the particulate filter 3 needs to be changed. Data relating to the flow resistance may also be saved in a database for later reference.

(9) The system according to the invention may also comprise separate pressure sensing devices for sensing the differential pressures P.sub.1 and P.sub.2, respectively. The pressure sensing means may comprise any kind of known pressure sensing device suitable for measuring differential pressures under the conditions applicable in exhaust systems. It is preferable, but not necessary, that the measurements of the differential pressures P.sub.1 and P.sub.2 are performed simultaneously, since this ensures that the conditions under which the flow resistance R is determined are equivalent to those under which the volume flow of exhaust gas is determined. The pressure sensing device used to determine the second differential P.sub.2 in the shown embodiment has pressure inlet ports 9, 10 located upstream and downstream the SCR system 4. However, the pressure inlet port located downstream the SCR system 4 may be substituted for an atmospheric pressure inlet port.

(10) FIG. 3 illustrates very schematically an electronic control unit 11 comprising an execution means 12, such as a central processor unit (CPU), for executing a computer program. The execution means 12 communicates with a memory 13, for example of the type RAM, through a data bus 14. The control unit 11 also comprises a non-transitory data storing medium 15, for example in the form of a Flash memory or a memory of the type ROM, PROM, EPROM or EEPROM. The execution means 12 communicates with the data storing medium 15 through the data bus 14. A computer program comprising computer program code for implementing a method according to the invention is stored on the data storing medium 15.

(11) The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.