METHOD FOR TESTING THE EFFICIENCY OF AN EXHAUST LINE CATALYTIC CONVERTER FOR AN INTERNAL COMBUSTION ENGINE

Description

[0001] The present invention relates to a method for testing the efficiency of an exhaust line catalyst of a heat engine. The invention finds a particularly advantageous application with efficiency tests of motor vehicle catalysts carried out during after-sales service operations.

[0002] Pollutant emissions from internal combustion engines in motor vehicles are regulated by standards. Depending on the internal combustion engine technology, the regulated pollutants are carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter formed during fuel combustion in the combustion chamber and then emitted through the exhaust.

[0003] It is known to use a certain number of pollution control methods in the exhaust line of thermal engines to limit pollutant emissions. Thus, it is possible to install a catalyst placed upstream of a particulate filter. The catalyst is made from a material with reversible oxygen storage properties depending on the richness of the exhaust gases. The catalyst has an oxygen storage capacity, called "OSC" for "Oxygen Storage Capacity" in English. It allows oxygen to be stored when the engine is operating in lean mode (air / fuel ratio greater than 1) to restore it in rich mode (air / fuel ratio less than or equal to 1). The catalyst helps ensure the oxidation of carbon monoxide (CO) and unburned hydrocarbons (HC) and the reduction of nitrogen oxides (NOx).The oxygen storage capacity of the catalyst is an indicator of its aging because the older the catalyst, the less oxygen it is able to store.

[0004] It has been found through the analysis of catalysts returned for after-sales service that there are many cases of incorrect removal of the catalyst, which is costly for the vehicle manufacturer while the vehicle is still under warranty. This is due either to a lack of analysis (the repairer simply removes the catalyst as soon as a fault signal relating to the operation of the pollution control system is returned), or to a lack of knowledge.

[0005] Methods for testing the efficiency of a catalyst in a heat engine exhaust line are known from documents EP2772636A1 which corresponds to the preamble of claim 1 as well as EP3067527A1, US2016138506A1, WO2016146907A1, DE102008027575A1, which however require improvement.

[0006] The invention aims to effectively remedy this drawback by proposing a method for testing the efficiency of a catalyst of an exhaust line of a thermal engine, in particular of a motor vehicle, an upstream oxygen sensor and a downstream oxygen sensor being arranged respectively upstream and downstream of the catalyst, said method comprising: a step of operating the heat engine until its temperature reaches a minimum temperature threshold, a step of checking the operation of the oxygen sensors, and in the case where the oxygen sensors are operating correctly, said method further comprises: a step of operating the heat engine at a high speed, a step of controlling a return to an idle speed of the heat engine, a step of measuring a rise time of a voltage of the downstream sensor above a predetermined voltage threshold, and a step of determining a state of the catalyst as a function of the measured rise time of the voltage.

[0007] The invention thus makes it possible, thanks to the analysis of the duration of the rise in voltage of the downstream probe, to discriminate between a catalytic converter in good working order and a defective one. After-sales service repairers will thus avoid removing catalytic converters which would have been "wrongly" detected as defective by the control system. The invention also has the advantage of being able to be carried out by any garage using criteria which are easy to verify to determine the condition of the catalytic converter.

[0008] According to one implementation, in the case where the measured duration of the voltage rise of the downstream probe is less than a duration threshold, the catalyst is considered defective and in the case where the measured duration of the voltage rise is greater than the duration threshold, the catalyst is considered functional.

[0009] According to one implementation, the duration threshold is a fixed threshold that can be calibrated between 15s and 25s and is preferably of the order of 20s.

[0010] According to one implementation, the step of verifying the operation of the oxygen sensors consists of verifying: that the oxygen sensors do not return a fault signal, that a voltage of the upstream sensor is located within a first predefined range of values, and that the voltage of the downstream sensor is located within a second predefined range of values.

[0011] According to one implementation, the first predefined value range is between approximately 0.1V and 0.8V.

[0012] According to one implementation, the second predefined value range is between approximately 0.1V and 0.8V.

[0013] According to one implementation, the minimum temperature threshold of the heat engine is around 80 degrees Celsius.

[0014] According to one implementation, the high speed of the thermal engine is between 3000 rpm and 4000 rpm and is for example around 3500 rpm.

[0015] According to one implementation, the high speed of the thermal engine is maintained for a minimum duration of 10 seconds.

[0016] The invention also relates to a diagnostic tool configured for implementing the method for testing the efficiency of a catalyst in a heat engine exhaust line as previously defined.

[0017] The invention will be better understood by reading the following description and examining the accompanying figures. These figures are given only for illustrative purposes but in no way limit the invention. [ Fig. 1 ] There figure 1 is a schematic representation of an architecture of an exhaust line of a thermal engine comprising a catalyst whose operating state is to be verified via the implementation of the method according to the invention; [ Fig. 2 ] There figure 2 is a diagram of the different steps of the method for testing the efficiency of a heat engine catalyst according to the present invention.

[0018] There figure 1 schematically represents a part of an exhaust line 1 collecting the exhaust gases from a heat engine 2 fitted to a motor vehicle. The exhaust line 1 comprises a catalyst 3 arranged upstream of a particulate filter 4. The catalyst 3 and the particulate filter 4 are grouped in the same casing 5 connected to the rest of the line 1 by its ends (the figure only represents half of the casing 5 to make the catalyst 3 and the particulate filter 4 visible).

[0019] Catalyst 3 is made from a material with reversible oxygen storage properties depending on the richness of the exhaust gases. Catalyst 3 has an oxygen storage capacity, called "OSC" for "Oxygen Storage Capacity" in English. It allows oxygen to be stored when engine 2 is operating in lean mode (air / fuel ratio greater than 1) to be released in rich mode (air / fuel ratio less than or equal to 1). Catalyst 3 helps ensure the oxidation of carbon monoxide (CO) and unburned hydrocarbons (HC) and the reduction of nitrogen oxides (NOx). The oxygen storage capacity of catalyst 3 is an indicator of its aging because the older catalyst 3 gets, the less it is able to store oxygen.

[0020] The exhaust line 1 is also equipped with two oxygen probes 6, 7. An upstream probe 6 and a downstream probe 7 are arranged respectively upstream and downstream of the catalyst 3. These probes 6, 7 of known type may take the form of linear or stoichiometric type probes.

[0021] The following is described, with reference to the figure 2 , the method according to the invention for testing the efficiency of the catalyst 3 of the exhaust line 1. The various measurements detailed below can be carried out statically under no load in the workshop by installing an exhaust gas extraction pipe or outdoors.

[0022] This method comprises a step 100 of operating the heat engine 2 until its temperature T_mth reaches a minimum temperature threshold S_temp, for example of the order of 80 degrees Celsius. By "of the order of" is meant a variation of plus or minus 10% around this value. It should be noted that the temperature of the heat engine T_mth is the temperature of the coolant, in particular based on water and antifreeze, circulating in a corresponding circuit of the engine.

[0023] The operator then checks, in a step 101, the correct functioning of the probes 6, 7 by ensuring that the following three conditions C1-C3 are respected: Condition C1: probes 6, 7 do not return a fault signal. Condition C2: for a stoichiometric type probe, a voltage V_am of the upstream probe 6 is located in a first predefined range P1 of values ​​between approximately 0.1V and 0.8V. The voltage value V_am of the upstream probe 6 is not stable. Alternatively, for a linear lambda type probe, it is ensured that the output signal corresponding to the inverse of the richness of the air-fuel mixture is between 0.9 and 1.11. Condition C3: a voltage V_av of the downstream probe 7 is located in a second predefined range P2 of values ​​between approximately 0.1V and 0.8V. The output voltage V_av of the downstream probe may be at a stable level or oscillate. The first range P1 and the second range P2 are identical here but could alternatively be different depending on the probe model used.

[0024] If one of the three conditions C1-C3 is not verified, it is then necessary to stop the test (see step 102) and to look for the origin of the problem on the probes 6, 7 themselves, the connectors, or the electrical harness, etc. It is therefore not necessary to replace the catalyst 3 under any circumstances.

[0025] If probes 6, 7 are functioning correctly, the process is continued (see step 103).

[0026] For this purpose, the heat engine 2 is operated in a step 104 at a high no-load speed R_mth of between 3000 rpm and 4000 rpm and for example of the order of 3500 rpm. The chosen speed must be maintained in particular with stable positioning of the accelerator pedal. Preferably, the high speed of the heat engine 2 is maintained for a minimum duration of 10 seconds.

[0027] Then, in a step 105, a return to an idle speed of the thermal engine 2 between 700 rpm and 900 rpm is commanded, in particular by releasing the accelerator pedal. While remaining at idle speed, the repairer then measures, in a step 106, a duration D_rem of rise of the voltage V_av of the downstream probe 7 above a predetermined voltage threshold, in particular of the order of 0.6V.

[0028] In the absence of a fault signal, particularly of the "P0420" type for a Peugeot engine ("Registered trademark"), it is not necessary to change catalyst 3.

[0029] In the presence of a fault signal, the state of the catalyst 3 is determined according to the duration D_rem of the rise of the measured voltage V_av. In the case where the measured duration D_rem of the rise of the voltage V_av of the downstream probe 7 is less than a duration threshold S_rem, the catalyst 3 is considered defective and must therefore be replaced (see step 107). In the case where the measured duration D_rem of the rise of the measured voltage of the voltage V_av is greater than the duration threshold S_rem, the catalyst 3 is considered functional (see step 108). There is therefore no need to replace it. The duration threshold S_rem is a fixed threshold that can be calibrated between 15s and 25s and is preferably of the order of 20s.

[0030] The method according to the invention can be implemented manually by a mechanic or automatically by a diagnostic tool which can check the operation of the probes via interaction with the engine computer, directly control the engine speed without having to act on the accelerator pedal, and determine the duration D_rem of the rise in the voltage V_av of the downstream probe 7 to deduce the state of the catalyst 3.

Claims

1. Method for testing the effectiveness of a catalyst (3) of an exhaust line (1) of a thermal engine (2) in particular of a motor vehicle, an upstream oxygen probe (6) and a downstream oxygen probe (7 ) being arranged respectively upstream and downstream of the catalyst (3), characterized in that said process comprises: - a step (100) of starting the heat engine (2) until its temperature ( T_mth ) reaches a minimum temperature threshold ( S_temp ), - a step (101) of checking the operation of the oxygen probes (6, 7), and in the case where the oxygen probes (6, 7) operate correctly, said method further comprises : - a step (104) of starting the heat engine (2) at a high speed, - a step (105) of controlling a return to an idling speed of the thermal engine (2), - a step (106) of measuring a duration ( D_rem ) of rising a voltage ( V_av ) of the downstream probe (7) above a predetermined voltage threshold, and - a step (107, 108) of determining a state of the catalyst (3) as a function of the measured duration ( D_rem ) of voltage rise ( V_av ).

2. Method according to claim 1, characterized in that in the case where the measured duration ( D_rem ) of voltage rise ( V_av ) of the downstream probe (7) is less than a duration threshold ( S_rem ), the catalyst (3 ) is considered defective and in the case where the measured duration ( D_rem ) of voltage rise ( V_av ) is greater than the duration threshold ( S_rem ), the catalyst (3) is considered functional.

3. Method according to claim 2, characterized in that the duration threshold ( S_rem ) is a fixed threshold that can be calibrated between 15s and 25s and is preferably of the order of 20s.

4. Method according to any one of claims 1 to 3, characterized in that the step (101) of checking the operation of the oxygen probes (6, 7) consists of checking: - that the oxygen probes (6, 7) do not send a fault signal, - that a voltage ( V_am ) of the upstream probe (6) is located in a first predefined range of values (P1), and - that the voltage ( V_av ) of the downstream probe (7) is located in a second predefined range of values (P2).

5. Method according to claim 4, characterized in that the first predefined range of values (P1) is between approximately 0.1V and 0.8V.

6. Method according to claim 4 or 5, characterized in that the second predefined value range (P2) is between approximately 0.1V and 0.8V.

7. Method according to any one of claims 1 to 6, characterized in that the minimum temperature threshold ( S_temp ) of the heat engine is of the order of 80 degrees Celsius.

8. Method according to any one of claims 1 to 7, characterized in that the high speed ( R_mth ) of the heat engine (2) is between 3000 rpm and 4000 rpm and is for example of the order of 3500 rpm.

9. Method according to any one of claims 1 to 8, characterized in that the high speed ( R_mth ) of the heat engine (2) is maintained for a minimum duration of 10 seconds.

10. Diagnostic tool characterized in that it is configured for implementing the method of testing the efficiency of a catalyst (3) of an exhaust line (1) of a heat engine (2) as defined according to any of the preceding claims.