METHOD FOR OPTIMAL CONTROL OF THE CATALYTIC SYSTEM OF THE EXHAUST LINE OF MOTOR VEHICLES

Abstract

The invention relates to a method for controlling the catalytic window of the exhaust line of motor vehicles with thermal engines (M), said line comprising, upstream, a first three-way redox catalyst (TWC) associated, on the one hand, with a first oxygen sensor (S1) and, on the other hand, with a second oxygen sensor (S2) and, downstream, a second three-way redox catalyst (UFC), said window being modulated from the quantity of oxygen detected in the first catalyst by the first oxygen sensor (S1), characterized in that the catalytic window is modulated by taking into account, in addition, the quantity of oxygen present jointly in the second catalyst (UFC) and detected by said second oxygen sensor (S2). Figure 1

Description

Title of the invention: METHOD FOR OPTIMALLY CONTROLLING THE CATALYTIC SYSTEM OF THE EXHAUST LINE OF MOTOR VEHICLES

[0001] The invention relates, in general, to the field of catalytic treatment of exhaust gases from motor vehicles with thermal engines and is more particularly concerned with a method for controlling and optimizing the catalytic treatment.

[0002] Internal combustion engines in motor vehicles, and in particular spark-ignition engines powered by petrol, are today necessarily equipped with an exhaust line incorporating a catalytic system for treating polluting gaseous emissions.

[0003] Such a catalytic system integrates a first block provided with a 3-way redox catalyst (called TWC for "Three Way Catalyst") and a particulate filter (called GPF). Generally, a first proportional oxygen sensor is mounted upstream of this block and a second binary oxygen sensor is mounted downstream. This system also integrates a second block provided with a complementary 3-way catalyst (called UFC for "Under Floor Catalyst") possibly associated with an ammonia storage device (called ASC) which is mounted after the second binary oxygen sensor. At the end of this exhaust line there is also a third oxygen sensor (or Nox / NH3) forming a richness sensor.

[0004] The control of the catalytic treatment by command control is carried out from a richness regulation function (oxygen rate) upstream and downstream of the system. In order to optimize the neutralization of polluting emissions in the catalytic system, there is for each operating point of the engine a richness range making it possible to maximize the efficiency of conversion of the main pollutants (HC, CO, NOx, NH3) by catalysis.

[0005] Current control methods for gasoline thermal engines consist of defining a richness setpoint to be regulated upstream of the catalysts in order to obtain maximum efficiency in converting polluting gaseous emissions. This setpoint, commonly called the "catalytic window" or "TWC window", is defined both for each operating point of the engine and according to the aging state of the catalyst. The positioning of this window is generally around the stoichiometric zone so that the system is capable of converting all pollutants.

[0006] The main objective of the invention is to regulate this setpoint or richness window as precisely as possible under stabilized conditions. However, the calibration of this setpoint requires a compromise on the conversion efficiencies of the catalyst. Indeed, by placing oneself on the rich side (that is to say, with a mixture richness > 1) the conversion of NOx is favored to the detriment of the other CO / HC / NH3 pollutants and conversely on the lean side (with a mixture richness < 1).

[0007] Patent EP1706622B1 describes an exhaust line comprising two catalysts intended to ensure the purification of exhaust gases. The first catalyst acts at start-up. The second catalyst is a three-way catalyst.

[0008] These two catalysts can trap oxygen and thus oxidize carbon monoxide (CO) and / or hydrocarbons (HC) contained in the exhaust gases. Furthermore, when an oxidized component such as NOx is present in these exhaust gases, it is reduced, which makes it possible to purify the gaseous emissions containing this pollutant. Jointly, the oxygen produced during this reduction reaction is captured by the two catalysts.

[0009] However, the method for controlling the catalytic system described in this patent provides, per engine operating point, a phase with a window setpoint located only on the rich side or a window setpoint phase located only on the lean side, which does not make it possible to obtain an optimal setpoint level.

[0010] In this context, the invention sought to optimize the window setpoint from a new functionality using the implementation of the second block provided with the three-way complementary catalyst (UFC). The method of the invention thus consists of modulating the window setpoint as a function of the quantity of oxygen stored in this catalyst.

[0011] Consequently, under stabilized conditions, instead of applying single setpoints (per operating point), it now becomes possible, thanks to the invention, to apply dynamic window setpoints. Therefore, the method of the invention aims to define optimal window setpoints which can be, jointly, rich and / or lean.

[0012] This object is achieved, according to the invention, by means of a method for controlling the catalytic window of the exhaust line of motor vehicles with thermal engines, said line comprising, upstream, a first three-way redox catalyst associated, on the one hand, with a first oxygen sensor and, on the other hand, with a second oxygen sensor and, downstream, a second three-way redox catalyst, said window being modulated from the quantity of oxygen detected in the first catalyst by the first oxygen sensor, characterized in that modulates the catalytic window taking into account, in addition, the quantity of oxygen jointly present in the second catalyst and detected by said second oxygen probe.

[0013] According to a preferred embodiment of the method of the invention, when the quantity of oxygen present in the second catalyst is greater than a determined threshold, a high richness window is applied to minimize NOx emissions and when the quantity of oxygen in the second catalyst is less than said threshold, a leaner richness window is applied to limit HC / CO / NH3 emissions.

[0014] According to an alternative embodiment of the method of the invention, said catalytic window is weighted by positioning it between the high richness window and the leaner richness window as a function of the average quantity of oxygen present in the second catalyst.

[0015] Preferably, the transition is made from the high richness window to the leaner richness window when the internal temperature in the second catalyst is sufficient.

[0016] According to an advantageous characteristic of the method of the invention, the catalytic window is modulated by taking into account, in addition, the electrical voltage at the terminals of the second oxygen sensor.

[0017] Another object of the invention is a computer program intended to be loaded into an on-board computer for the implementation of the piloting method as defined above.

[0018] Yet another subject of the invention is a motor vehicle with a thermal engine equipped with an exhaust line comprising, upstream, a first three-way redox catalyst associated, on the one hand, with a first oxygen sensor and, on the other hand, with a second oxygen sensor and, downstream, a second three-way redox catalyst and an on-board computer associated with a computer program for implementing a control method as defined above.

[0019] The method of the invention effectively complements the traditional method of adjusting the catalytic window which was based on calibration according to the operating point of the engine and the aging state of the first catalyst.

[0020] The invention makes it easier to calibrate the catalytic window and thus allows more robust control of the pollution control treatment than the traditional process and more efficient in terms of conversion of polluting emissions passing through the exhaust line, whatever the conditions.

[0021] Furthermore, the method of the invention is simple to implement in a control device.

[0022] Other characteristics and advantages of the invention will emerge on reading the description which follows, with reference to the appended figures, for which:

[0023] [Fig-1] is a schematic view of an embodiment of an exhaust line of a motor vehicle with a thermal engine to which the control method of the invention is applied.

[0024] [Fig.2] is a block diagram of an embodiment of the control method of the invention applied to the exhaust line of [Fig.l].

[0025] [Fig.3] is a graph illustrating the implementation of the control method of [Fig.2].

[0026] Naturally, the method of implementing the method of the invention described below and illustrated by the appended figures is given only as a non-limiting example. It is explicitly provided within the scope of the invention that different methods can be proposed and combined to propose others.

[0027] The invention relates to the catalytic system of the exhaust lines of motor vehicles with thermal engines and is more particularly concerned with the optimized control of such a system.

[0028] The objective of the invention is to propose means for regulating the richness (the oxygen level) upstream and downstream of the catalytic system. In order to optimize the neutralization of polluting emissions in this catalytic system, there is for each operating point of the engine a richness range making it possible to maximize the efficiency of conversion of the main pollutants (HC, CO, NOx, NH3) by catalysis.

[0029] Current control methods for gasoline thermal engines consist of defining a setpoint or richness window which should be regulated upstream of the catalysts in order to obtain maximum efficiency in converting gaseous emissions.

[0030] Generally speaking and as shown in [Fig.l], the exhaust line of a combustion engine M to which the control method of the invention is intended to be applied comprises, upstream, a first three-way redox catalyst (designated TWC) coupled to a particulate filter (designated GPF). This first catalyst is associated on the one hand with a first oxygen sensor SI of the proportional type and, on the other hand, with a second oxygen sensor S2 of the binary type. Downstream, the line comprises a second redox catalyst (UFC) also three-way connected here in series with the first catalyst (TWC) and coupled to an ammonium storage device (ASC). Where appropriate, the exhaust line further comprises, at its outlet end, a third sensor S3 or an oxygen and / or NOx / NH3 sensor.

[0031] Traditionally, the richness window is modulated from the quantity of oxygen detected in the first catalyst (TWC) by the first oxygen SI probe.

[0032] The invention consists of providing a new functionality which uses the implementation of the second three-way catalyst (UFC) to modulate the richness setpoint.

[0033] More precisely, the method of the invention modulates the catalytic window by taking into account, in addition to the quantity of oxygen already stored in the first catalyst (TWC), the quantity of oxygen present jointly in the second catalyst (UFC) and detected by the second oxygen probe S2.

[0034] According to a preferred embodiment of the invention, the method provides that when the quantity of oxygen present in the second catalyst (UFC) is greater than a determined threshold, a high richness window is applied to minimize NOx emissions and, conversely, when the quantity of oxygen in the second catalyst (UFC) is lower than said threshold, a leaner richness window is applied to limit HC / CO / NH3 emissions.

[0035] Thus, under stabilized conditions, instead of applying a single setpoint (per operating point), it becomes possible to apply a dynamic setpoint.

[0036] According to an alternative implementation of the method of the invention, it is possible to weight the catalytic window by positioning it between the high richness window and the leaner richness window as a function of the average quantity of oxygen present in the second catalyst (UFC).

[0037] Preferably, the method provides for only moving from the high richness window to the leaner richness window when the internal temperature in the second catalyst is sufficient.

[0038] According to an advantageous characteristic of the method of the invention, the catalytic window is modulated by taking into account, in addition, the electrical voltage at the terminals of the second oxygen sensor.

[0039] With the implementation of the second catalyst (UFC), the adjustment of the catalytic window was duplicated to take into account the state of this catalyst. The method of the invention thus makes it possible to have three adjustment modes which are illustrated by [Fig.2],

[0040] The first adjustment mode corresponds to the known traditional mode which relies solely on the first active catalyst (TWC) capable of converting the pollutants, the second catalyst being inactive.

[0041] The second adjustment mode uses the two active catalysts (TWC + UFC) but with this second catalyst saturated with oxygen.

[0042] The third adjustment mode still uses the two active catalysts (TWC + UFC) but with this second catalyst devoid of oxygen.

[0043] An alternative adjustment mode can be implemented by weighting (of the barycenter type) by positioning itself between the two previous adjustments according to the current quantity of oxygen and stored on average in the second catalyst (UFC).

[0044] When the second catalyst (UFC) contains a large amount of oxygen, it is able to easily treat HC / CO / NH3 pollutants and it becomes possible to calibrate a slightly richer catalytic window in order to minimize NOx emissions. During this phase, the oxygen in the second catalyst is gradually consumed. When the amount of oxygen present becomes too low, it is then necessary to switch to a leaner catalytic window to limit HC / CO / NH3 emissions without generating more NOx.

[0045] Overall, this method of implementing the process proves to be more robust than the traditional continuous adjustment method and more effective for the treatment of emissions than a method using a single catalyst.

[0046] [Fig.3] illustrates the principle of modulation of the catalytic window (example of binary calibration, by applying a setting with the first TWC catalyst or the second UFC catalyst, and without interpolation between the two catalysts). As long as the quantity of oxygen stored in the second catalyst (UFC) is greater than a previously determined threshold, the “UFC hot and full of O2” setting is applied.

[0047] As soon as the quantity of oxygen (OSL for "Oxygen Storage Level") present in the second catalyst (UFC) falls below this threshold, the "UFC hot and empty O2" setting is then applied, which is a slightly leaner setpoint than the previous setpoint. The catalytic window will therefore modulate according to the change in the quantity of oxygen (OSL) stored in the second catalyst (UFC).

[0048] The method of the invention applies identically to the evaluation of the electrical voltage setpoint of the probe S2 defined by the downstream richness regulation because the catalytic window and the voltage setpoint are always closely linked.

Claims

Claims

1. Method for controlling the catalytic window of the exhaust line of motor vehicles with thermal engines (M), said line comprising, upstream, a first three-way redox catalyst (TWC) associated, on the one hand, with a first oxygen sensor (SI) and, on the other hand, with a second oxygen sensor (S2) and, downstream, a second three-way redox catalyst (UFC), said window being modulated from the quantity of oxygen (OSL) detected in the first catalyst by the first oxygen sensor (SI), characterized in that the catalytic window is modulated by taking into account, in addition, the quantity of oxygen (OSL) present jointly in the second catalyst (UFC) and detected by said second oxygen sensor (S2).

2. Method according to claim 1, characterized in that when the quantity of oxygen present in the second catalyst (UFC) is greater than a determined threshold, a high richness window is applied to minimize NOx emissions and when the quantity of oxygen in the second catalyst is lower than said threshold, a leaner richness window is applied to limit HC / CO / NH3 emissions.

3. Method according to the preceding claim, characterized in that said catalytic window is weighted by positioning it between the high richness window and the leaner richness window as a function of the average quantity of oxygen present in the second catalyst (UFC).

4. Method according to claim 2 or 3, characterized in that one passes from the high richness window to the leaner richness window when the internal temperature in the second catalyst is sufficient.

5. Method according to one of the preceding claims, characterized in that the catalytic window is modulated by taking into account, in addition, the electrical voltage at the terminals of the second oxygen sensor (S2).

6. Computer program intended to be loaded into an on-board computer for implementing the piloting method according to one of the preceding claims, when said program operates on a computer.

7. Motor vehicle with thermal engine equipped with an exhaust line comprising, upstream, a first three-way redox catalyst (TWC) associated, on the one hand, with a first oxygen sensor (SI) and, on the other hand, with a second oxygen sensor (S2) and, downstream, a second three-way redox catalyst (UFC) and an on-board computer associated with a computer program according to claim 6 for implementing a control method according to one of claims 1 to 5.

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