Method for treating pollutants using a three-way catalyst when starting a combustion engine - Patents.com

Abstract

The present invention relates to a method involving the treatment of pollutants emitted by a vehicle having a heat engine, in which a catalytic means (3) is heated, characterized in that the amount of oxygen (OS) in the catalytic means (3) is controlled to exceed a minimum amount of oxygen (OS1) by injecting air upstream of said catalytic means (3).

Description

[Technical field]

[0001] The present invention relates to the field of catalytic converters intended to treat the exhaust gases of internal combustion engines, in particular the exhaust gases emitted by vehicles, with a view to reducing the emissions at engine start of pollutant components such as carbon monoxide, nitrogen oxides or unburnt hydrocarbons. [Background technology]

[0002] In order for the catalytic converter to effectively treat these pollutant emissions in the exhaust, the temperature of the catalytic converter needs to be above a threshold light-off temperature, which is typically achieved by heating the catalytic converter by the exhaust gases passing through it.

[0003] The time it takes for the catalytic converter to reach this temperature can be long, resulting in the emission of significant amounts of raw gas containing pollutants, the amounts of which tend to be very high either relative to enforced standards or relative to self-regulatory targets that are lower than the amounts in the standards.

[0004] It is known practice, for example from patent application FR2778206A1, to achieve an increase in the temperature of the catalyst by heating the gases entering the catalyst prior to engine start.

[0005] However, it has been found that this solution does not provide a satisfactory reduction in pollution because it does not regulate the amount of oxygen in the catalyst. Thus, immediately after engine start-up, the hydrocarbon throughput can be low due to a lack of oxygen, even when the temperature is high. Summary of the Invention

[0006] The present invention seeks to reduce emissions of pollutant components by combining catalyst temperature regulation and oxygen regulation.

[0007] In view of the above, the subject of the invention is a method for the treatment of pollutants emitted by a combustion engine, in which a catalytic means is heated and the amount of oxygen in the catalytic means is adjusted so that it remains higher than a minimum amount of oxygen by injecting air upstream of the catalytic means.

[0008] Preferably the catalytic means is heated above a preheat threshold temperature before the amount of oxygen in the catalytic means is adjusted.

[0009] For example, heating of the catalytic means may be performed before the engine is authorized to start.

[0010] Advantageously, the adjustment of the amount of oxygen in the catalytic means is carried out before the engine is approved to be started.

[0011] According to one embodiment, adjusting the amount of oxygen and heating the catalytic means occurs after a request to start the engine is detected.

[0012] In one embodiment, the amount of oxygen in the catalyst means is maintained above a stoichiometric oxygen concentration threshold after starting the engine.

[0013] Advantageously, the heating element is switched off when the temperature of the catalytic means exceeds a steady state temperature threshold after starting the engine.

[0014] The method may further comprise a step during which the amount of oxygen in the catalytic means is increased above a stoichiometric oxygen concentration threshold after starting the engine and once the heating element has been switched off.

[0015] Preferentially, the amount of oxygen in the catalytic means is adjusted to maintain the amount of oxygen substantially near the stoichiometric oxygen concentration threshold after said stoichiometric concentration threshold is exceeded.

[0016] The invention also relates to a method, wherein a pre-heating grid of a heating element is heated to a minimum grid temperature before the catalytic means is heated with said heating element.

[0017] In this way, it is possible to achieve satisfactory operation of the catalyst system right from the engine start, which then results in a significant reduction in the amount of pollutants emitted, especially when a vehicle equipped with such a catalyst system is driven in city areas on short trips that lead to frequent starts.

[0018] The invention will be better understood from a detailed study of some embodiments thereof considered as non-limiting examples and illustrated by the accompanying drawings, in which: [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic diagram of a system used to effect the treatment of pollutants emitted by a combustion engine type vehicle using catalytic means; [Diagram 2] FIG. 2 is a diagram of an example implementation of the processing system of FIG. 1. [Diagram 3] FIG. 3 details the steps of the implementation of FIG. 2 prior to engine start-up. [Figure 4] FIG. 3 details the steps of the implementation of FIG. 2 after engine start-up. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Reference is made to FIG. 1 which illustrates one embodiment of a system used to effect the treatment of pollutants emitted by a vehicle having a combustion engine 1 using catalytic means 3 placed after the exhaust 4 from the engine 1.

[0021] The catalyst 3 comprises a three-way catalytic converter 3 with so-called "precious" metals such as palladium, platinum or rhodium. The catalyst 3 treats the exhaust gases leaving the exhaust pipe 6 using three parallel chemical reactions: oxidizing carbon monoxide, oxidizing hydrocarbons and reducing nitrogen oxides.

[0022] Several catalysts may be provided in series.

[0023] Catalyst 3 includes an impregnated surface (known as a "washcoat") containing a cerium oxide-based compound that can store or release oxygen very quickly to facilitate catalytic reactions.

[0024] The catalyst 3 is only effective above about 400 degrees Celsius. In the prior art, a short drive does not allow enough time for the catalytic converter to warm up satisfactorily.

[0025] The system for the treatment of pollutants is therefore additionally equipped with heating means 5 which release heat via the Joule effect on the catalyst 3, for example via a pre-heating grid consisting of an electrically resistive metal element through which an electric current flows. The heating element 5 can be placed upstream of the catalyst 3 in the gas flow direction or above the catalyst 3.

[0026] The treatment of pollutants also makes use of air circulation means 2 designed to deliver air upstream of the catalyst 3, for example an air circulation pump 2 equipped with a compressor blowing into exhaust lines 4,6.

[0027] The control means is configured to establish a connection between the probes S1, S2 for the oxygen content and the temperature installed upstream or downstream of the catalyst 3 and an intersystem communication network, e.g. having a CAN bus, for controlling the heating means 5 and the air pump 2 via a computer, e.g. embodied by a vehicle computer equipped with a processor.

[0028] For example, the upstream probe S1 controls the concentration of fuel relative to air or relative to oxygen in the gas leaving the engine 1.

[0029] A downstream probe S2 may be provided to monitor the oxygen concentration Os at the outlet of the catalyst 3. The concentration is defined as the level of fuel in the air as estimated or measured by the probes S1, S2 relative to the stoichiometric level of fuel in the air in the catalyst 3. The stoichiometric ratio is the level of fuel in the air that leads to a near-perfect chain of catalytic reactions.

[0030] FIG. 2 illustrates an example of an implementation of a pollutant treatment system.

[0031] This implementation starts with step R0, where an intention to imminently switch on the engine 1 is detected, for example via detection of a request to start the vehicle or the presence of a user.

[0032] To that end, a user's desire to start the engine may be detected when the anti-start system is disabled, when the vehicle ignition is switched on, or otherwise when a vehicle door, particularly the driver's door, is opened.

[0033] Alternatively, the presence of a user in the seat is detected by detecting contact with the vehicle seat using, for example, infrared detection or by detecting the user's eyes.

[0034] The control means may be programmed via the vehicle dashboard control interface or via a remote device such as a smart phone. In particular, the control means is configured to enable the system to be used throughout step M0 without starting the vehicle.

[0035] For example, the control means are configured to schedule, at a given time, each day the performance of step R0, ie the confirmation of the intention to start the engine, which leads to step M0.

[0036] The control means may be configured to take into account information regarding the amount of available electrical energy in a charge store of the vehicle, for example a vehicle battery, and if this information is available, step R0 may lead to exiting the strategy by ceasing to use the pollution treatment system prior to use of the engine. In the context of use where the vehicle battery is close to being discharged, the command to heat the catalyst during step M0 may therefore be modified or even cancelled in order to give priority to propelling the vehicle.

[0037] When the control means recognise a request confirming the intention to start the engine 1, the method proceeds to step C1 of step M0.

[0038] Step M0, detailed in FIG. 3, includes steps C1, C2, E1, E2 and C3, which are used to prepare favorable conditions for catalysis before engine 1 is allowed to start during step D0.

[0039] During step C1, the computer estimates the temperature TCAT of the catalyst 3 from at least one measurement from temperature probes S1, S2 upstream and / or downstream of the catalyst 3, and compares this temperature of the catalyst 3 against a preheat threshold TCAT1 of the order of 400 degrees Celsius.

[0040] The catalyst 3 may thus be at the light-off temperature for the catalytic reaction when the engine 1 is started during step D0.

[0041] The computer 7 may further be configured to determine, for example during step C1, whether all the implementation means 2, 3, 5 and sensors S1, S2 that the vehicle 1 is equipped with and that are going to be required are functional. If appropriate, step C1 leads to step C2.

[0042] If a failure of one of the required sensors S1, S2 or the heating element 5 is detected, then preparation may be made for a degraded mode which is declared during step C1.

[0043] The degraded mode of step C1 consists, for example, in issuing information such as exiting the strategy, i.e. enabling a direct start without preheating or air injection, and displaying an error signal on the instrument panel of vehicle 1.

[0044] The first comparison step C1 is repeated at regular time intervals, for example every 10 milliseconds.

[0045] If the preheating temperature TCAT1 is reached during step C1, this leads to step C2, otherwise it leads to step C3.

[0046] Step C2 consists in checking, using a temperature probe, that the preheat grid is at a temperature higher than the minimum grid temperature TGRID. If appropriate, step C2 is continued to step E1, otherwise to step E2.

[0047] For maximum efficiency of the catalytic action at the start of the engine 1, the pre-heating of the heating grid 5 occurs simultaneously with the operation of the air circulation pump 2 so that the heat generated by the heating grid can be transferred to the catalyst 3 installed downstream of said heating grid even in the absence of a gas flow coming from the engine 1.

[0048] Step E1 therefore consists in supplying power to the heating element 5 and switching off or keeping the pump 2 switched off. Step E1 proceeds to step C2. As long as the heating element 5 has not reached the temperature TGRID, the supply of power through the preheating grid is maintained or increased.

[0049] Step E2 consists in switching on or keeping on the heating element 5 and in switching on or keeping on the pump 2. The air sent upstream of the catalyst 3 is then therefore drawn from the oxygen-rich atmosphere and circulates through a preheating grid to enable the catalyst 3 to be preheated prior to starting the engine 1.

[0050] During step C3, the amount OS of oxygen in the catalyst 3 is compared with an oxygen content OS1 of the order of 8 to 10 moles per cubic meter. As long as the oxygen content OS is lower than the content OS1, step C3 proceeds to step E2, otherwise it continues to step D0.

[0051] Step D0 consists in enabling and carrying out the starting of the engine 1. At the time of starting, the pump 2 may be switched off and the operation of the heating element 5 may be maintained. Step D0 is followed by a set of steps E3 and M1.

[0052] The set of steps M1 includes steps E3, C4, E4, E5 and C5, E6, E7 which are executed successively at regular intervals, for example every 10 milliseconds.

[0053] Step E3 consists in stopping the injection of air as soon as the engine 1 has started, for example by switching off the pump 2. Step E3 is followed by steps C4 and C5, which are executed in parallel.

[0054] In order to combust the carbon monoxide remaining in the exhaust gases, the temperature TCAT of the catalyst 3 must be higher than a temperature threshold TCAT2 of about 600 degrees Celsius, and the amount of oxygen OS in the catalyst must exceed an oxygen content threshold OS2 of about 1 to 3 moles per cubic meter.

[0055] The catalyst 3 is heated thermochemically by an exothermic catalytic reaction which complements the electrical heating that takes place.

[0056] Step C4 consists in comparing the temperature TCAT of the catalyst 3 with a threshold value TCAT2. If TCAT exceeds TCAT2, the heating element 5 is switched off and the heat addition is replaced by a thermochemical addition, otherwise the method returns to step E5, during which the heating element 5 is switched on or kept switched on and the current through it is maintained or increased.

[0057] Step C5 is a check whether the oxygen content OS of the catalyst 3 has fallen below an oxygen content threshold OS2. If the oxygen content OS of the catalyst 3 falls below the threshold OS2, step C5 is continued to step E6, otherwise step C5 goes to step E7.

[0058] Step E6 consists in removing carbon monoxide from the exhaust gas. For that purpose, a concentration set point greater than 100 percent, including between 110 and 140 percent, is imposed on the concentration in the catalyst 3, or in other words the oxygen content OS is increased above the stoichiometric amount. This step proceeds to step C5 as long as the heating element 5 is switched on, i.e. as long as the method does not go past step E4. Once step E4 has been passed, step E6 may be maintained for 5 to 60 seconds before proceeding to step C5. Step E6 is therefore carried out only once after engine start.

[0059] During step E7, the engine reaches a steady state and the conventional concentration regulation of the treatment system is activated, for example a concentration set point of substantially 100 percent is sent to the control means.

[0060] In this manner, the system evaluates and verifies the oxygen requirements of the catalyst and manages the achievement of proper temperatures before and after engine start-up to limit emissions of hydrocarbons, nitrogen-containing compounds and carbon monoxide.

Claims

1. A method for the treatment of pollutants emitted by a combustion engine (1), in which a catalytic means (3) is heated, characterized in that the amount of oxygen (OS) in said catalytic means (3) is adjusted so that said amount of oxygen (OS) remains higher than a minimum amount of oxygen (OS1) by injecting air upstream of said catalytic means (3), said heating of said catalytic means (3) and said adjustment of the amount of oxygen (OS) in said catalytic means (3) are performed before it is approved to start said combustion engine (1) and after a request to start said combustion engine (1) is detected, The heating of the catalytic means (3) and the adjustment of the amount of oxygen (OS) in the catalytic means (3) are heating said catalytic means (3) to a predetermined threshold temperature by a heating element (5) located upstream of said catalytic means (3); injecting air upstream of said catalytic converter (3) when the temperature of said catalytic converter (3) exceeds said predetermined threshold temperature; starting the combustion engine (1) when the amount of oxygen (OS) in the catalytic means (3) is higher than the minimum amount of oxygen (OS1); A method comprising:

2. 2. The method of claim 1, wherein the amount of oxygen (OS) in the catalytic means (3) is kept higher than a stoichiometric oxygen concentration threshold (OS2) after starting the combustion engine (1).

3. 3. The method according to claim 1 or 2, wherein the heating element (5) is switched off when the temperature (TCAT) of the catalytic means (3) exceeds a steady-state temperature threshold (TCAT2) after starting the combustion engine (1).

4. 4. The method according to claim 3, wherein the amount of oxygen (OS) in the catalytic means (3) is increased above a stoichiometric oxygen concentration threshold (OS2) after starting the combustion engine (1) and once the heating element (5) is switched off.

5. 5. The method according to claim 2 or 4, wherein the amount of oxygen (OS) in the catalytic means (3) is adjusted to keep the amount of oxygen (OS) substantially near the stoichiometric oxygen concentration threshold (OS2) after exceeding the stoichiometric oxygen concentration threshold (OS2).

6. 6. The method according to any one of claims 1 to 5, wherein a pre-heating grid of the heating element (5) is heated to a minimum grid temperature (TGRID) before the catalytic means (3) is heated with the heating element (5).

Images