Internal combustion engine unit comprising an exhaust circuit with a nitrogen oxide concentration sensor

Abstract

Engine unit comprising at least one internal combustion engine, an exhaust circuit comprising a duct opening onto the outside and exhaust gas depollution devices including a last depollution device (23, 23'), and at least one nitrogen oxide concentration sensor (50), arranged downstream of said last depollution device (23, 23'), said sensor (50) comprising a head (500) at least partly included inside a portion of said duct (205'), the latter containing a deflector device located upstream of said sensor head, and downstream of said last depollution device, said deflector device comprising a flap (51) and motorized actuating means (513) driving said flap into an inclined position of partial opening in order to accelerate the speed of the exhaust gases arriving at the head of said sensor. Figure to be published with the abstract: Fig. 3

Description

Title of the invention: Internal combustion engine unit comprising an exhaust circuit with a nitrogen oxide concentration sensor

[0001] The invention relates to the field of exhaust circuits of an engine group comprising an internal combustion engine and an exhaust circuit comprising a nitrogen oxide concentration sensor. The internal combustion engine may be of the spark ignition type (petrol) or compression ignition type (diesel).

[0002] A non-limiting example of a known engine group for a motor vehicle is illustrated schematically by figure [Fig.l]. This engine group comprises an internal combustion engine, an air intake circuit and an exhaust circuit as well as a low-pressure partial recirculation circuit of the exhaust gases at the engine intake, said engine being a gasoline engine for which the subject of the invention finds a particularly advantageous application, although not limitingly.

[0003] As illustrated, the gasoline engine is a combustion engine 10 comprising four in-line cylinders. Said engine is associated with an air intake circuit 1 comprising an air filter 11, a flow meter 110, the compressor of a turbocharger, a supercharged gas cooler 13, an intake gas intake valve (throttle body 12), an intake manifold (distributor 14).

[0004] The engine is also associated with an exhaust circuit 2 which comprises an exhaust manifold 20, the turbocharger turbine, and a plurality of exhaust gas depollution devices. According to this example of a gasoline engine, said depollution devices comprise two combined electrically heated catalysts 21, for example of the three-way catalyst type, then a particulate filter 22, and finally another three-way catalyst 23, generally mounted under the body (under the floor). According to the example, the circuit comprises three oxygen sensors, or “O2” sensors 200, 201, 202 for measuring the oxygen concentration in the exhaust gases.

[0005] This exhaust circuit also comprises in this example a partial recirculation circuit of the exhaust gases 2b at the engine intake, more precisely a low pressure recirculation circuit. However, it is not specifically necessary for the object of the invention.

[0006] The engine group comprises a plurality of temperature sensors and pressure sensors not shown in the figure [Fig.l].

[0007] To limit the quantities of pollutants emitted by vehicles, for example in compliance "Euro" standards which set the limits of emissions in the European Union, and in particular the upcoming "Euro 7" standard, it is necessary to have a nitrogen oxide concentration sensor in the exhaust gas circuit, located after all the pollution control elements, which will be useful to the vehicle's on-board control system, called "OBM" (English acronym for "On Board Monitoring"), regardless of the type of engine. The said nitrogen oxide concentration sensor is also commonly called “NOx sensor” or “NOx probe”.

[0008] This NOx sensor will be used in particular to manage the regulation of the richness (fuel-air ratio) in the combustion chamber of the engine. In the case of gasoline, this richness can only oscillate over a very narrow range around 1, the air (oxygen)-fuel dosage having to remain close to stoichiometry.

[0009] One problem is the difficulty of having sufficient gas speeds on the NOx sensor, to have a satisfactory response time, due to the very low gas flow rates at low speed and / or low load points, typically at idle. This problem arises more particularly in the case of a gasoline engine in which the engine torque is regulated by adjusting the air flow, which is generally not the case in diesel except in very specific cases such as the regeneration of a particulate filter.

[0010] The invention thus aims to resolve this drawback.

[0011] To this end, the invention proposes a motor group comprising: - at least one internal combustion engine, - an exhaust circuit comprising a conduit capable of guiding from upstream to downstream the exhaust gases emitted by said engine towards the outlet orifice of the conduit opening onto the outside, and comprising exhaust gas depollution devices including a last depollution device (before the outlet orifice of said conduit), and at least one nitrogen oxide concentration sensor (NOx sensor), arranged downstream of said last depollution device (and upstream of said outlet of said conduit), said sensor comprising a head at least partly included inside a portion of said conduit, said head extending partially inside said portion of conduit. According to the invention, said portion of conduit contains a deflector device located upstream of said sensor head, and downstream of said last decontamination device. Said deflector device comprises a generally flat flap, arranged inside said portion of conduit, comprising two opposite faces composing a distal face and a proximal face to said sensor head, and said flap being inclinable relative to the longitudinal direction of said portion of conduit, said flap occupying at least one fully open position oriented along the longitudinal direction of said portion of conduit and an inclined position of partial opening, said deflector device comprising motorized actuating means driving said flap into said inclined partial opening position in order to accelerate the speed of the exhaust gases arriving at the head of the NOx sensor, in particular when said exhaust gases circulate at low flow rate in said portion of conduit.

[0012] More particularly, said sensor head extends partially inside said portion of conduit and such that its longitudinal (main) direction is substantially perpendicular to the longitudinal direction of said portion of conduit.

[0013] More particularly, said motorized actuating means comprise a pivot axis secured transversely to the flap, with a direction substantially perpendicular to the longitudinal (main) direction of the sensor head and substantially perpendicular to the longitudinal direction of said portion of conduit, this pivot axis making it possible to tilt said flap in said portion of conduit.

[0014] Preferably according to the invention, the flap is arranged at a distance from the head of the NOx sensor which is less than the internal diameter of said portion of conduit.

[0015] Preferably, said inclined position of partial opening of the shutter corresponds to an opening angle of the shutter of between 15 and 25 degrees, and more particularly between 18 and 22 degrees, the position of total opening of the shutter corresponding to an opening angle of 90 degrees.

[0016] Preferably, the distal face, opposite the face proximal to the head of the sensor, is substantially convex, in other words its convexity is turned towards the side from which the gas flow arrives at the flap, so that the gases are deflected on either side of said flap in the portion of conduit and accelerated when they arrive at the level of the head of the sensor.

[0017] Advantageously, said inclined position of partial opening of the flap is optimized according to a combination of the ratio of said distance between the flap in the fully closed position and the head of the sensor to the internal diameter of said portion of conduit, and the angle of partial opening of said flap, in order to obtain a rapid response time of the measurement of the NOx sensor, in accordance with the reality of the composition of the gases, for low exhaust gas flow rates, in particular for engine speeds at idle. More particularly, the combination is established so that the speed of said gases arriving at said head of the sensor can reach a value greater than a threshold, in particular at least approximately 5 m / s, preferably at least approximately 7 m / s.

[0018] Said distance between said flap and said sensor head is more particularly defined along the longitudinal direction of said portion of conduit, by the distance between the center of said flap and the median longitudinal axis of the head of said sensor.

[0019] Preferably according to the invention, the ratio of said given distance between the flap and the head of the sensor to the internal diameter of said portion of conduit (expressed in the same unit of measurement) is less than or equal to 1 in combination with an angle partial opening which is of the order of 20 degrees (for example, plus or minus 2 degrees).

[0020] In particular, said shutter has the shape of a parabolic disc.

[0021] The engine group comprises at least one internal combustion engine, which may be naturally aspirated or preferably turbocharged (supercharged), assisted or not by electric motors. In addition, one or more computers may be used to operate the entire engine group.

[0022] Preferably, said at least one internal combustion engine is a gasoline engine.

[0023] The invention also relates to a motor vehicle comprising an engine unit as described above.

[0024] In particular, said nitrogen oxide concentration sensor is connected electronically to the on-board control system of the vehicle (OBM) and the positions of the flap of said deflector device are controlled by control means integrated into or coupled to said control system (OBM).

[0025] The depolluting devices for the post-treatment of the exhaust gases produced by the engine, resulting from the combustion of the fuel / intake air mixture, may comprise a catalytic converter for depolluting the exhaust gases and preferably also a particulate filter for treating the fine particles present in the exhaust gases, as well as a three-way catalyst as the last depolluting device before the outlet of the exhaust duct.

[0026] Other features and advantages of the invention will emerge from reading the description given below of a particular embodiment of the invention, given for informational purposes but not as a limitation, with reference to the attached drawings.

[0027] [Fig.l] schematically illustrates a known engine group for a motor vehicle, comprising a gasoline engine connected to an exhaust line;

[0028] [Fig.2] illustrates a portion of the exhaust line conduit comprising a deflector device and a NOx sensor, in accordance with the invention, suitable for an engine group as illustrated in [Fig.l];

[0029] [Fig.3] illustrates in close-up the deflector device and the NOx sensor head in the portion of exhaust duct illustrated in [Fig.2];

[0030] [Fig.4a] illustrates by a profile view, a representation of the exhaust gases arriving at the head of a NOx sensor at the outlet of the last depollution device in the same portion of conduit as that represented [Fig.2] but no deflector device is included therein, to determine the speed of the gases arriving at this sensor head,

[0031] [Fig.4b] illustrates by a profile view, a representation of the exhaust gases in the exhaust conduit arriving at the head of a NOx sensor, comprising a deflector device with its flap in the fully open position, to determine the speed of the gases arriving at this sensor head, for a portion of conduit conforming to figures 2 and 3.

[0032] [Fig.4c] illustrates by a profile view, a representation of the exhaust gases in the exhaust duct arriving at the head of a NOx sensor, comprising a deflector device with its flap in the partially open position, to determine the speed of the gases arriving at this sensor head, for a portion of duct conforming to figures 2 and 3.

[0033] The concepts of "upstream" and "downstream" relate to the direction of circulation of the exhaust gases in the exhaust line, symbolized by the arrow G or G', the gases circulating from the combustion chamber of the engine towards the exhaust outlet, in other words towards the open end of the exhaust line conduit expelling said gases towards the outside, into the atmosphere.

[0034] In comparison with the example of the engine group represented [Fig.l], commented on above, and with reference to [Fig.2], the NOx sensor 50, the head 500 of which is inside the portion of conduit 205' of the exhaust circuit, will be located downstream of the last depolluting device 23', in this case identical to the three-way catalyst 23. The NOx sensor is obviously located before the outlet orifice of the exhaust circuit.

[0035] The head 500 of said NOx sensor extends partially inside said duct portion 205', and its main longitudinal direction SS' is substantially perpendicular to the longitudinal direction XX' of said duct portion 205'. According to the example, the median longitudinal axis of said head corresponds to the main longitudinal direction SS' of said head, as illustrated in [Fig.3].

[0036] A deflector device is installed inside the duct portion 205', upstream and close to the head 500 of the NOx sensor II. It comprises a flap 51, generally flat, which has the shape of a parabolic disc, comprising two opposite faces 510, 520, forming a convex distal face 510 and a proximal face 511, relative to said head 500 of said NOx sensor.

[0037] Said flap 51 is substantially centered in said portion of conduit 205'.

[0038] Said shutter 51 can be controlled by a motorized actuator comprising a pi axis vote 513 shown in the figures, oriented along the transverse direction of the flap d0-d0', such an actuator being known per se. The transverse direction of the flap d0-d0' is substantially perpendicular to the main longitudinal direction of the sensor head and substantially perpendicular to the longitudinal direction of said duct portion. This actuator makes it possible to control the tilting movement of the flap 51, around its pivot axis 513 in the duct portion 205, for example from its fully open position to a partially open position, according to a given opening angle, and vice versa, in response to a request by the vehicle's on-board control system ("OBM").

[0039] According to the example, the flap can be provided to occupy two positions. The first position is a fully open position in which the flap 51 is inclined for an opening angle of 90 degrees, in other words the flap is “horizontal” in the duct, its plane being oriented along the longitudinal direction XX' of said portion of duct. The second position is a partially open position, in which the flap is inclined for an opening angle strictly between 0 and 90 degrees (0 and 90 are excluded values), according to the example of the order of 20 degrees.

[0040] The flap is in the first position (fully open) for engine speeds where the exhaust gas flow rate is sufficient to have gas speeds satisfactory for the measurement accuracy of the NOx sensor, i.e. greater than a threshold, for example at least 7 m / s at the head of the NOx sensor depending on the type of sensor used.

[0041] The flap is inclined in the second position for an engine speed at low exhaust gas flow rate, typically at idle, in order to increase the speed of the exhaust gases arriving at the head of the NOx sensor in order to reach gas speeds higher than said threshold, for example at least 7 m / s, at the level of the head of the NOx sensor.

[0042] With reference to [Fig. 3], “D” designates the internal diameter of the portion of duct 205' at which the NOx sensor is mounted, “L” designates the distance between the center of the flap 512 (at the intersection with the pivot axis of the flap 513), and the median longitudinal axis S-S' of the head 500 of the NOx sensor 50. Said opening angle of the flap 51 in the duct is designated by “a”, with a=0° for a flap which would be completely closed, its direction plane drdi' being oriented along the direction ZZ' of the portion of duct perpendicular to the longitudinal direction XX' of said portion of duct (and to the direction of the pivot axis 513), and a=90° for a completely open flap, i.e. “horizontal” in said portion of duct, its plane being oriented along the longitudinal direction XX' of said portion of duct.The opening angle “a” of the flap 51 is therefore defined as the angle between the direction of its main direction plane drdi' (distal face side) and the direction ZZ' of the portion of conduit perpendicular to the longitudinal direction XX' of said portion of conduit and perpendicular to the direction of the pivot axis 513 of said flap.

[0043] Aerodynamic studies were conducted to measure gas speeds at the head of the NOx sensor for different values ​​of opening angle “a” of the flap 51 and for different L / D ratios (L and D being expressed in the same unit of measurement) to determine the best combination of L / D and “a” making it possible to obtain a gas speed greater than the target threshold, for example at least 7 m / s, for different engine speeds, in particular at low gas flow rate (12 kg / h at a temperature of 230°C), specifically at idle where the speeds are low.

[0044] From these studies, in particular for an “idle” regime, at low gas flow (12kg / h on the engine used), it appears that a large opening angle, of the order of 60 degrees, does not provide any improvement to the gas speed. For small flap opening angles (less than 5 degrees), the gas speed is increased and can reach the target threshold (7m / s for the type of sensor used), as was observed by mounting the NOx sensor with an L / D ratio of between 1.3 and 1.5, therefore strictly greater than 1. Additional studies have, however, shown that if the L / D ratio is greater than 1, problems of pressure drop, particularly in the portion of the duct with the deflector, can quickly arise.

[0045] The best combination is obtained for an L / D ratio less than or equal to 1, and an opening angle substantially equal to 20 degrees (distance “L” between the flap and the head of the sensor on the internal diameter of said portion of conduit D (L and D being expressed in the same unit of measurement). In other words, a slightly less closed angle is adopted and the flap is brought closer to the sensor.

[0046] Figures 4a, 4b, 4c represent, by profile views, the gases circulating at a given instant, in a portion of pipe equipped with a NOx sensor, for a study determining gas speeds obtained at the level of the head of the NOx sensor for different configurations and at an engine speed at idle (at low flow): without deflector device for [Fig.4a], with the deflector device and L / D <1, the flap being in the fully open position for [Fig.4b], or the flap being in an intermediate inclined position with a=20.1° for [Fig.4c]. In the first two configurations, the gas speed is 3.6 m / s, while in the last configuration the speed reached is 8.1 m / s, which confirms the result mentioned previously.

[0047] From [Fig.4c], it can be observed that, when the flap is inclined in the second position (partial opening), the flow of exhaust gases (arrow G') arrives on the slightly convex distal face 510 of the flap 51, said flap 51 being inclined according to the opening angle "a" of approximately 20 degrees, so that these gases are deflected on either side of said flap and accelerated when they arrive in the portion of conduit at the level of the head of the sensor.

[0048] The speed of the exhaust gases arriving at the head of the NOx sensor is of the order of 7 m / s. This is therefore favorable to a rapid response time of the measurement of the NOx sensor, in accordance with the reality of the concentration of nitrogen oxides in the gases, for low exhaust gas flow rates, in particular for engine speeds at idle.

[0049] As soon as the gas speed is at least 7m / s, the flap can be kept fully open to limit the impact of exhaust backpressure on engine performance. These studies confirm that a deflector device with a flap that can only hang in two positions (fully open and partially open inclined position) is sufficient to achieve the objective of a speed above the target threshold, for example at least 7m / s, which is economically advantageous because it is less expensive than a continuously variable position deflector.

Claims

Claims

1. Engine group comprising: - at least one internal combustion engine, - an exhaust circuit comprising a duct capable of guiding from upstream to downstream the exhaust gases emitted by said engine towards the outlet orifice of the duct opening onto the outside, and comprising exhaust gas depollution devices including a last depollution device (23, 23'), and at least one nitrogen oxide concentration sensor (50), arranged downstream of said last depollution device (23, 23'), said sensor (50) comprising a head (500) at least partly included inside a portion of said duct (205'), said head extending partially inside said portion of duct,and said duct portion (205') containing a deflector device comprising a generally planar flap (51) arranged inside said duct portion and which has two opposite faces forming a distal face (510) and a proximal face (511) to said sensor head, and said flap being tiltable relative to the longitudinal direction (XX') of said duct portion, said flap occupying at least one fully open position oriented along the longitudinal direction of said duct portion and an inclined partial open position, characterized in that said deflector device is located upstream of said sensor head and downstream of said last depollution device, said deflector device comprising motorized actuating means (513) driving said flap into said inclined partial open position in order to accelerate the speed of the exhaust gases arriving at the head of said sensor,said flap (51) being arranged at a distance (L) from the head of said sensor which is less than or equal to the internal diameter (D) of said portion of conduit, and said inclined position of partial opening of the flap corresponding to an opening angle (a) of the flap of between 15 and 25 degrees, the position of total opening of the flap corresponding to an opening angle of 90 degrees.,

2. Engine group according to claim 1, characterized in that said inclined position of partial opening of the flap corresponds to an opening angle (a) of the flap of between 18 and 22 degrees.

3. Motor group according to one of claims 1 to 2, characterized in that the distal face (510) of the flap, opposite the proximal face of the head of the sensor, is substantially convex.

4. Engine unit according to one of claims 1 to 3, characterized in that said inclined position of partial opening of the flap is optimized according to a combination of the ratio of said distance between the flap in the fully closed position and the head of the sensor on the internal diameter of said portion of conduit, and the angle of partial opening of said flap, so that the speed of said gases arriving at said head of the sensor can reach a value greater than a threshold, in particular at least approximately 5 m / s, and preferably at least approximately 7 m / s.

5. Engine group according to claim 4, characterized in that the ratio of said given distance between the flap and the head of the sensor to the internal diameter of said portion of conduit is less than or equal to 1 and said partial opening angle is of the order of 20 degrees.

6. Motor unit according to one of claims 1 to 5, characterized in that said motorized actuating means comprise a pivot axis (513) secured transversely to the flap (51), of direction substantially perpendicular to the longitudinal direction (SS') of the head of said sensor and substantially perpendicular to the longitudinal direction (XX') of said portion of conduit, this pivot axis making it possible to tilt said flap in said portion of conduit.

7. Engine group according to one of claims 1 to 6, characterized in that said internal combustion engine is a gasoline engine.

8. Motor vehicle, characterized in that it comprises a motor unit according to one of claims 1 to 7.

9. Motor vehicle according to claim 8, characterized in that said nitrogen oxide concentration sensor (50) is connected electronically to the on-board control system of the vehicle, and the positions of the flap (51) of said deflector device are controlled by control means integrated into or coupled to said control system.

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