Method for controlling a naturally aspirated spark-ignition internal combustion engine equipped with a three-way catalyst

Abstract

This method for controlling a naturally aspirated internal combustion engine (1) with spark ignition comprising an exhaust manifold (12) integrated into a cylinder head (13) of the engine (1) and provided with a three-way catalyst (5) configured to treat polluting emissions from the engine (1) and positioned in the vicinity of an exhaust outlet (3a) of the cylinder head (13) comprises steps of: - determining a load demand, - determining a first temperature, - controlling a complete opening of a throttle body (10) if the load demand is equal to or greater than a predetermined threshold value and as long as the first temperature is lower than a second temperature representative of a predetermined maximum threshold, and - controlling a partial closing of the throttle body (10) if the load demand is lower than the predetermined threshold value or if the first temperature is greater than or equal to the second temperature.Figure for abstract: Figure 1.

Description

Title of the invention: Method for controlling an atmospheric type spark-ignition internal combustion engine equipped with a three-way catalyst Technical field

[0001] The technical field of the invention is the control of spark-ignition internal combustion engines, and more particularly, the control of such engines with a view to reducing the emission of polluting species. Previous techniques

[0002] In internal combustion engines of the spark-ignition type, particularly used in motor vehicles and running on gasoline, it is known to carry out the depollution of the combustion gases of the engine by a three-way type catalyst mounted on the engine exhaust.

[0003] It is useful to heat the three-way catalyst as quickly as possible after cold starting the engine so that the catalyst operates as early as possible in its catalytic window in which it reduces the nitrogen oxides produced in the combustion gases of the engine, and it oxidizes the unburned hydrocarbons and carbon monoxide. It is thus known to integrate the exhaust manifold into the cylinder head of the engine and to place the catalyst in a position close to the engine, that is to say as close as possible to the exhaust outlet of the cylinder head in order to minimize heat losses.

[0004] However, although favorable for rapidly heating the catalyst, these architectures can lead to very significant temperature increases of the catalyst in the operating zones corresponding to high loads or high engine speeds. These temperature increases can degrade the durability of the catalyst, i.e. its mechanical reliability. The loss of durability results initially in an increasingly marked degradation of the catalyst treatment performance, then in its mechanical ruin.

[0005] In order to reduce the exhaust temperature so as to contain it below a maximum threshold value admissible for the durability of the catalyst, while maintaining the level of performance of the engine, it is common to enrich the air-fuel mixture, sometimes to richness values ​​greater than 1.20. However, this enrichment practice results in excessive emissions of carbon monoxide due to the lack of oxygen, thus compromising the effectiveness of the three-way catalyst with regard to the treatment of nitrogen monoxide. By effectiveness of a catalyst is meant, in a manner known per se, the proportion of polluting molecules of a given variety that the catalyst manages to treat.

[0006] Furthermore, the use of these thermal enrichments is progressively restricted by increasingly strict regulations concerning pollutant emissions and by bans on bypass devices ("Defeat Device" in English).

[0007] Without the use of thermal enrichment, the engine performance at full load shows a marked decrease, with an estimated loss of approximately 10% of maximum power compared to engines using thermal enrichment. Disclosure of the invention

[0008] In view of the above, the invention aims to provide a method for controlling a naturally aspirated internal combustion engine with spark ignition, making it possible to effectively treat polluting emissions while maintaining good engine performance in the event of high torque demands.

[0009] The subject of the invention is a method for controlling a naturally aspirated internal combustion engine with spark ignition comprising an exhaust manifold integrated into a cylinder head of the engine and provided with a three-way catalyst configured to treat polluting emissions from the engine and positioned in the vicinity of an exhaust outlet of the cylinder head.

[0010] The method comprises steps of: - determination of an engine load demand, - determination of a first catalyst temperature, - comparison of the first temperature with a second predetermined temperature representative of a predetermined maximum catalyst temperature threshold not to be exceeded, - comparison of the engine load demand with a predetermined threshold value representative of a full load demand, - commanding a complete opening of a throttle body of the engine if the engine load demand is equal to or greater than the predetermined threshold value and as long as the first temperature is lower than the second temperature, - control of a partial closing of the throttle body if the engine load demand is lower than the predetermined threshold value or if the first temperature is higher than or equal to the second temperature.

[0011] Such a method makes it possible to ensure efficient treatment of pollutant emissions, while maintaining optimal engine performance during high torque demands. In addition, the method protects the durability of the catalyst and therefore its long-term treatment efficiency.

[0012] Preferably, during the method, the engine is controlled to operate with a unit richness setpoint representative of the stoichiometry. Such an engine allows to reduce fuel consumption compared to engines using thermal enrichments.

[0013] Advantageously, the partial closing of the throttle body is controlled so as to contain the first catalyst temperature below the second catalyst temperature.

[0014] According to one embodiment, the determination of the first catalyst temperature is carried out using a predetermined estimated catalyst temperature model.

[0015] According to another embodiment, the determination of the first temperature of the catalyst is carried out from a value measured by a catalyst temperature sensor.

[0016] According to one feature, the engine load demand is determined from a value of the depression of an accelerator pedal or a value of pressure exerted on the pedal.

[0017] According to another aspect, the invention relates to a controlled-ignition internal combustion engine of the atmospheric type comprising an exhaust manifold integrated into a cylinder head of the engine and provided with a three-way catalyst configured to treat polluting emissions from the engine and positioned in the vicinity of an exhaust outlet of the cylinder head, the engine further comprising an electronic control unit configured to implement a method as defined above.

[0018] According to another aspect, the invention relates to a motor vehicle equipped with an engine as defined above. Brief description of the drawings

[0019] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0020] [Fig-1] is a schematic view of an engine according to an exemplary embodiment of the invention;

[0021] [Fig.2] is a flowchart illustrating the different stages of an adjustment process of the engine of [Fig.l] according to an exemplary embodiment of the invention; and

[0022] [Fig.3] illustrates an example of implementation of the method of [Fig.2]; Detailed description of at least one embodiment

[0023] In the example illustrated in [Fig.l], the internal combustion engine 1 is of the naturally aspirated spark ignition type. In other words, the engine 1 is not supercharged by a turbocharger or a volumetric compressor.

[0024] The heat engine 1 sucks in air in the direction of arrow E via an intake duct 2, and discharges its exhaust gases via a duct exhaust 3 in order to direct them towards a pollution control device 4. The pollution control device 4 comprises a three-way catalyst 5 and preferably a particle filter 6. The exhaust pipe 3 is provided upstream of the pollution control device 4 with a proportional richness sensor 7 making it possible to regulate the richness of the air-fuel mixture of the engine 1.

[0025] The fuel, for example gasoline, a mixture of gasoline and ethanol, or even pure ethanol, is supplied to the engine 1 by means of an injection system (not shown), for example a direct injection system which comprises a fuel rail common to the cylinders 8 and at least one fuel injector per cylinder capable of injecting the fuel directly into each of the cylinders 8. In the example illustrated in [Fig.l], the engine is provided with three cylinders arranged in line. For example, the engine 1 may comprise a different number of cylinders. Other cylinder configurations may be envisaged, without departing from the scope of the invention.

[0026] At the outlet of the pollution control device 4, the exhaust gases are discharged into the outside atmosphere in the direction of the arrow S.

[0027] In the air intake duct 2, in a non-limiting manner, there may be found an air filter 9 which makes it possible to eliminate the dust contained in the air and an intake flap 10, or butterfly valve 10 which makes it possible to regulate the flow admitted into the engine 1 by more or less obstructing the intake duct 2. The air is distributed to the cylinders 8 through an intake manifold 11 arranged downstream of the butterfly valve 10.

[0028] An exhaust manifold 12 is directly integrated into a cylinder head 13 of the engine 1 in order to minimize the distance between the exhaust valves of the cylinders 8 and the catalyst 5. The catalyst 5 is thus positioned in the vicinity of an exhaust outlet 3a of the cylinder head 13. This configuration allows a rapid rise in temperature of the catalyst by maximizing the number of calories available for heating the catalyst 5.

[0029] As illustrated in [Fig.l], the catalyst 5 may be equipped with means for determining a parameter representative of the temperature of the exhaust gases passing through it, for example the temperature of the catalyst 5 itself, measured by a temperature sensor 5a. Alternatively, it remains possible for the catalyst 5 not to be equipped with a temperature sensor 5a. In this case, it is possible to estimate the temperature of the catalyst 5 from a predetermined physical model. For example, such a physical model can estimate the temperature of the catalyst 5 from an outside air temperature, the mass flow rate of the inlet air, the ignition advance and the richness of the air-fuel mixture.

[0030] The engine 1 further comprises an electronic control unit 14 configured to control the various elements of the engine 1 from data collected by sensors at different locations in the engine.

[0031] The electronic control unit 14 comprises a calculation module 15, a measurement module 16 and a control module 17.

[0032] The measurement module 16 is for example capable of receiving the temperature measurements from the temperature sensor 5a.

[0033] The control module 17 is for example capable of controlling the fuel injection system and the opening and closing of the throttle body 10.

[0034] A method of controlling a motor according to the invention will now be described with reference to Figures 2 and 3.

[0035] [Fig.2] illustrates the different steps of a method for controlling an internal combustion engine 1 of a motor vehicle according to an exemplary embodiment of the invention.

[0036] The method is in particular implemented by means of an electronic control unit 14 of the engine 1.

[0037] The method begins with a step 20 of determining a load request from the engine 1. The load request from the engine 1 generally corresponds to the “driver's desire to accelerate”, materialized for example by a value of the depression of an accelerator pedal of the vehicle or the pressure exerted on said pedal.

[0038] The method continues with a step 21 of determining a first temperature T1 of the catalyst 5. As indicated previously, when the catalyst is provided with a temperature sensor 5a, the electronic control unit 14 determines the first temperature T1 from a measured value of the temperature of the catalyst 5 from the temperature sensor 5a. In the case where the catalyst is not provided with a temperature sensor 5a, the electronic control unit 14 estimates the first temperature T1 of the catalyst 5 from a predetermined physical model contained in a memory of the electronic control unit 14, from a temperature of the outside air, the mass flow rate of the inlet air, the ignition advance and the richness of the air-fuel mixture.

[0039] During the following comparison step 22, the first temperature T1 is compared on the one hand with a second predetermined temperature T2 and the engine load demand is compared on the other hand with a predetermined threshold value.

[0040] The second predetermined temperature T2 is representative of a predetermined maximum temperature threshold Tmax of the catalyst 5 not to be exceeded to ensure a predefined minimum durability of the catalyst. The predetermined maximum threshold Tmax is for example defined statistically by the manufacturer of the catalyst and may have a value such as 950°C.

[0041] The predefined minimum durability of the catalyst corresponds for example to a rate of maximum permissible failure of a catalyst population for a predetermined mileage traveled by vehicles equipped with the catalysts. It may correspond to a minimum catalyst treatment efficiency, more precisely, to a minimum residual treatment efficiency statistically observable at full load of a catalyst population for a mileage traveled.

[0042] The predetermined threshold value is representative of a full load demand.

[0043] If the engine load demand is equal to or greater than the predetermined threshold value and as long as the first temperature T1 does not exceed the second temperature T2, the electronic control unit 14 commands a complete opening of the throttle body 10 of the engine 1 (step 23). The complete opening of the throttle body 10 makes it possible to maximize the load admitted into the engine 1 and thus to significantly increase the performance of the engine 1.

[0044] If the load demand of the engine 1 is lower than the predetermined threshold value or if the first temperature T1 is higher than the second temperature T2, the electronic control unit 14 commands a partial closure of the throttle body 10 of the engine 1 (step 24). The partial closure of the throttle body 10 makes it possible to lower the temperature of the exhaust gases of the engine 1. The partial closure of the throttle body 10 is commanded so as to contain the first temperature T1 of the catalyst 5 below the second temperature T2 for the entire duration of the process. In other words, the degree of closure of the throttle body 10 is controlled so that the temperature T1 of the catalyst does not exceed the second temperature T2. Such a control can use, for example, predetermined maps linking the degree of closure of the throttle body to the exhaust gas temperatures for each operating point of the engine 1.

[0045] It should be noted that during the method of the invention, the engine 1 is controlled to operate with a unit richness setpoint representative of the stoichiometry.

[0046] [Fig.3] illustrates an example of implementation of the method of [Fig.2].

[0047] Curve 30 represents the variation over time of the first temperature Tl of the catalyst 5.

[0048] Curve 31 illustrates the variation over time of the percentage of opening of the throttle body. A zero percentage of opening corresponds to a complete closure, while a percentage of opening of 100% indicates a complete opening of the throttle body 10.

[0049] Curve 32 illustrates the variation over time of the percentage of depression of the accelerator pedal. A zero percentage of depression corresponds to a release of the pedal, while a percentage of depression of 100% is representative of a full load demand.

[0050] [Fig.3] highlights two acceleration phases, during which the driver requires a full engine load.

[0051] A first acceleration phase 33 takes place between the times t1 and t1'. During this phase, the complete opening of the throttle body 10 is controlled as long as the first temperature T1 of the catalyst 5 does not exceed the second temperature T2 representative of the predetermined maximum threshold Tmax not to be exceeded to ensure a predefined minimum durability of the catalyst 5 and therefore a minimum long-term treatment efficiency. It should be noted that the complete opening of the throttle body 10 is controlled over the entire duration of the first acceleration phase 33.

[0052] A second acceleration phase 34 takes place between times t2 and t2'. The second acceleration phase 34 is longer than the first acceleration phase 33 and it is observed that the first temperature T1 of the catalyst 5 reaches the value of the second temperature T2 at time t3. From then on, the partial closing of the butterfly housing 10 is commanded, so as to contain the first temperature T1 below the second temperature T2, guaranteeing the durability of the catalyst 5, and thus, statistically, that is to say with a known uncertainty, its long-term treatment efficiency.

[0053] The method thus makes it possible to optimize the performance of the engine 1 in the acceleration phases 33, 34, without however degrading the treatment efficiency of the catalyst 5.

Claims

Claims

1. Method for controlling an internal combustion engine (1) with spark ignition of the atmospheric type comprising an exhaust manifold (12) integrated into a cylinder head (13) of the engine (1) and provided with a three-way catalyst (5) configured to treat polluting emissions from the engine (1) and positioned in the vicinity of an exhaust outlet (3a) of the cylinder head (13), said method being characterized in that it comprises steps of: - determining a load demand of the engine (1), - determining a first temperature (T1) of the catalyst (5), - comparing the first temperature (T1) with a second predetermined temperature (T2) representative of a predetermined maximum temperature threshold (Tmax) of the catalyst (5) not to be exceeded, - comparing the load demand of the engine (1) with a predetermined threshold value representative of a full load demand,- controlling a complete opening of a throttle body (10) of the engine (1) if the load demand of the engine (1) is equal to or greater than the predetermined threshold value and as long as the first temperature (T1) is lower than the second temperature (T2), and - controlling a partial closing of the throttle body (10) if the load demand of the engine (1) is lower than the predetermined threshold value or if the first temperature (T1) is greater than or equal to the second temperature (T2).,

2. Method according to claim 1, during which the engine (1) is controlled to operate with a unit richness setpoint representative of the stoichiometry.

3. A method according to claim 1 or 2, wherein the partial closure of the butterfly housing (10) is controlled so as to contain the first temperature (T1) of the catalyst (5) below the second temperature (T2) of the catalyst (5).

4. A method according to any one of claims 1 to 3, wherein the determination of the first temperature (Tl) of the catalyst (5) is carried out using a predetermined estimated temperature model of the catalyst (5).

5. Method according to any one of claims 1 to 3, in which the determination of the first temperature (Tl) of the catalyst (5) is carried out from a value measured by a temperature sensor (5a) of the catalyst (5).

6. A method according to any one of claims 1 to 5, wherein the load demand of the engine (1) is determined from a value of the depression of an accelerator pedal or a value of pressure exerted on said pedal.

7. A naturally aspirated internal combustion engine (1) comprising an exhaust manifold (12) integrated into a cylinder head (13) of the engine (1) and provided with a three-way catalyst (5) configured to treat polluting emissions from the engine (1) and positioned in the vicinity of an exhaust outlet (3a) of the cylinder head (13), said engine (1) further comprising an electronic control unit (14) configured to implement a method according to any one of claims 1 to 6.

8. Motor vehicle equipped with an engine (1) according to claim 7.

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