FR3085716A1 - DEVICE FOR DEPOLLUTING EXHAUST GASES FROM AN INTERNAL COMBUSTION ENGINE OF A MOTOR VEHICLE AND METHOD FOR CONTROLLING SUCH A DEVICE - Google Patents

Abstract

The invention relates to a device for cleaning up exhaust gases from an internal combustion engine of a motor vehicle, said device comprising a circuit for exhausting gases from the combustion of said combustion engine, comprising a main duct for exhaust (31) and a bypass duct (33) between an upstream bypass point (34) of the exhaust circuit, upstream of said gas probe (2), and a downstream bypass point (35) of the circuit exhaust, downstream of said gas probe (2); said exhaust circuit comprising in the vicinity of the upstream branch point (34) a set of valves (36, 37) adapted to, in a first position, authorize the passage of gases in the main duct (31) and prohibit the passage of gas in the bypass duct (33) and, in a second position, prohibit the passage of gases in the main duct (31) and allow the passage of gases in the bypass duct (33).

Description

Device for cleaning up exhaust gases from an internal combustion engine of a motor vehicle and method for controlling such a device

The present invention relates to a device for cleaning up exhaust gases from an internal combustion engine of a motor vehicle and a method for controlling such a device.

A motor vehicle with an internal combustion engine comprises an exhaust circuit 1 for the gases produced during the combustion of the fuel in the engine 3, also called the exhaust line. This exhaust line 1, with reference to FIG. 1, comprises processing means capable of cleaning up the gases before they are expelled from the motor vehicle. In particular, it is known to treat exhaust gases in a catalytic converter, triggering chemical reactions capable of transforming the most toxic constituents of exhaust gases (CO, NOx ...) into less toxic elements (H ₂ O, CO ₂ , N ₂ ...).

Such an exhaust line comprises gas sensors 2, generically called gas probe 2, or gas probe 2, for example a nitrogen oxide (NOx) probe associated with a nitrogen oxide trap or a catalyst for the selective reduction of nitrogen oxides (generally abbreviated as SCR, from the English Selective Catalytic Reduction) or an oxygen sensor, generally called a Lambda sensor.

To ensure correct detection of the gases present in the exhaust circuit, the gas probes 2 of the exhaust line 1 must reach a high operating temperature, approximately 700 ° C for a NOx probe and between 200 ° C and 600 ° C for a Lambda probe.

However, a known problem is that the gas probes, at their operating temperature, must not come into contact with any particle of water, at the risk of being damaged.

However, it is known that at the start of a journey, and more particularly during a cold start of a motor vehicle engine, an exhaust line can contain a large amount of condensed water to which steam is added. of water produced by the engine 3.

The usual practice is then to define, with reference to FIG. 2, a warm-up time 20 of the engine 3 corresponding to the reaching of a dew temperature, also called dew point 22, of the exhaust line (in English Dew Point). The dew point corresponds to a gas temperature, measured in the exhaust system, where the water present in the gases can no longer be deposited in liquid form, and therefore can no longer form a drop of water.

Once this dew temperature 22 has been reached, the gas probes are then heated, for a duration 21 of temperature rise, called in English light off 21, under the effect of a heating member, such as a heat resistence.

In other words, it is ensured that the dew point is reached by the exhaust gases in the exhaust circuit, in order to allow the temperature sensors to rise without the liquid water transported by the exhaust gases. exhaust or present in the stationary circuit cannot come into contact with them, which is a cause of failure of the gas sensors.

It is only after this light off period 21 that the methods of depolluting the gases from the exhaust line 1 can be implemented.

However, a problem with this solution of the prior art is that there is a significant delay at the start of the depollution of the gases, because it is necessary to wait until the cumulative delays of reaching the dew point 20 and the light off 21 have passed.

We know in particular the patent document US6781098 which describes a method of heating the exhaust line distinguishing the cold start of the engine from a warm restart, for which no heating time is necessary. Thus, when a hot start is detected, the pollution control can start quickly. However, this document does not solve the problem of a faster start of the depollution after a cold engine start.

There is therefore a need for a solution to allow earlier starting of the exhaust gas pollution control after the cold start of the engine of the motor vehicle.

To this end, a device for depolluting the exhaust gases of an internal combustion engine of a motor vehicle is proposed, said device comprising an exhaust circuit for the gases resulting from the combustion of said combustion engine, comprising a main duct. exhaust extending between a gas inlet and a gas outlet, the device comprising at least one polluting gas probe installed in said main gas exhaust duct.

The exhaust circuit further comprises a bypass duct between a bypass point upstream of the exhaust circuit, upstream of said gas probe, and a bypass point downstream of the exhaust circuit, downstream of said gas probe gas;

said exhaust circuit comprising, in the vicinity of the upstream branch point, a set of valves adapted to, in a first position, authorize the passage of gases in the main duct and prohibit the passage of gases in the branch duct and, in a second position, prohibit the passage of gases in the main duct and allow the passage of gases in the bypass duct.

Thus, the device makes it possible to isolate the probe from the exhaust gases and to increase the temperature, in parallel with reaching the dew point of the exhaust gases. Thus, we can reduce the delay in starting the exhaust gas cleaning by avoiding having to wait for the cumulative times of reaching the dew point and heating the gas probe.

Advantageously and in a nonlimiting manner, the set of valves comprises a first valve installed in the main conduit, downstream of said upstream bypass point and upstream of the gas probe, and a second valve in the bypass conduit. So we can control in a relatively simple way in which conduit the exhaust gases are oriented.

Advantageously and in a nonlimiting manner, the bypass duct extends in the vicinity of the main duct so that in the second position of the valve assembly, the gases passing through the bypass duct produce a heating of the bypass duct suitable for heat the main pipe in the vicinity of the gas probe by thermal conduction. Thus the temperature rise of the main pipe can be accelerated, in particular near the gas probe.

The invention also relates to a method for controlling a pollution control device as described above, repeatedly comprising:

- a step of acquiring the gas temperature in the vicinity of the gas inlet;

- a step of acquiring the temperature of the gas probe;

and in that it includes:

- a step of raising the temperature of the gas probe; and

a step of controlling said set of valves so that:

o when the temperature of the gases is higher than a dew point temperature the set of valves is positioned in its first position, allowing the passage of the gases in the main duct and preventing the passage of the gases in the bypass duct; and o when the temperature of the gases is lower than the dew point temperature, the set of valves is positioned in a second position preventing the passage of gases in the main duct and authorizing the passage of gases in the bypass duct.

Thus, the device according to the invention can be controlled relatively simply and quickly.

The invention also relates to a control member of a pollution control device as described above, adapted to implement the control method described above.

The invention also relates to an engine assembly comprising an internal combustion engine, a pollution control device as described above and a control member described above.

The invention also relates to a motor vehicle comprising an engine assembly described above.

Other particularities and advantages of the invention will emerge on reading the description given below of a particular embodiment of the invention, given by way of indication but not limitation, with reference to the appended drawings in which:

- Figure 1 is a schematic view of an exhaust circuit of the prior art;

- Figure 2 is a graph showing the waiting time before the start of depollution of gases according to the prior art;

- Figure 3 is a view of a pollution control device according to one embodiment; and

- Figure 4 is a graph showing the waiting time before the start of depollution of gases according to the embodiment of Figure 3;

With reference to FIG. 3, a motor vehicle, not shown, comprises an internal combustion engine 3, and a device for cleaning up exhaust gases from an internal combustion engine of a motor vehicle.

The pollution control device includes an exhaust circuit for gases 10 from the combustion of fuel in the internal combustion engine 3.

The exhaust circuit 10 comprises a main exhaust duct 31 extending between an inlet for the gases 30, through which the gases from the combustion of the fuel enter the engine 3, and an outlet for the gases 32, for example a gas vent opening.

The pollution control device comprises at least one polluting gas probe 2 installed in the main gas exhaust duct 31, which will be called more simply gas probe or gas probe. This gas probe, in this embodiment a nitrogen oxide probe, also called NOx probe, or NOx sensor.

A NOx probe operates at a temperature of approximately 700 ° C, so it is necessary to bring it to such a temperature for its measurements to be reliable.

However, the invention is not limited to this type of probe, an alternative embodiment of the invention may include an oxygen probe, also called a Lambda probe, which has an operating temperature range between 200 ° C. and 600 ° C. Also the temperature ranges can be adapted according to the type of gas probe used.

In order to allow the gas probe to rise in temperature without the probe being in contact with water which could damage it, for example water transported by the gases passing through the main duct 31, the exhaust circuit includes a bypass conduit 33.

The bypass duct 33 is installed between an upstream bypass point 34 of the exhaust circuit, upstream of the gas probe 2, and a downstream bypass point 35 of the exhaust circuit, downstream of the gas probe 2.

In the present invention, the term “upstream” means the position in the exhaust circuit oriented in the direction of the gas inlet 30, while the term “downstream” designates the position oriented in the direction of the outlet. gas 32.

In this embodiment, the bypass conduit constitutes a bypass of the exhaust circuit only for the gas probe around which it is installed. Also, by this embodiment, the aim is to isolate only the gas probe during the rise in temperature of the gases and of the probe.

However, the upstream bypass points 34 and before 35 can be positioned by a person skilled in the art, according to the needs for insulation of other components of the exhaust circuit.

In order to control the circulation of gases in the exhaust circuit 10, two valves 36, 37 are installed in the vicinity of the upstream bypass point 34: a first valve 36 in the main duct 31, in the vicinity of the upstream bypass point 34 , but downstream of this bypass point 34, and a second valve 37 in the bypass duct 33, in the vicinity of the upstream bypass point 34, but downstream of this bypass point 34.

According to an alternative embodiment, the second valve 37 can be positioned at any point of the bypass duct 33.

Likewise, the first valve 36 can be positioned at any point of the main duct 31 between the upstream bypass point 34 and the gas probe 2.

The two valves 36, 37 are controlled so that when a first valve is in the open position, the other is in the closed position.

Also, the exhaust circuit always includes, among the main duct 31 and the bypass duct 33, an open duct and a closed duct.

The two valves 36, 37 thus form a set of valves 36, 37 having two distinct operating positions:

a first position, authorizing the passage of gases in the main conduit 31 and prohibiting the passage of gases in the bypass conduit 33, in which the first valve 36 is open and the second valve 37 is closed and,

- A second position, prohibiting the passage of gases in the main conduit 31 and authorizing the passage of gases in the bypass conduit 33, in which the first valve 36 is closed and the second valve 37 is open.

Each valve 36, 37 is impermeable to fluids, gases and liquids, so that it is capable of preventing the passage of combustion gases in the main duct 31 or in the bypass duct 33 depending on its operating position.

The set of valves 36, 37 is electrically controlled by a control member, not shown, such as an on-board computer.

Thus, the device according to the invention makes it possible to control whether the gases coming from the combustion engine and entering the exhaust circuit by the gas inlet 30 are led into the main pipe, consequently passing in contact with the gas probe. , or if they are diverted to the bypass pipe, so as not to come into contact with the gas probe.

The bypass conduit 33 is installed near the main conduit 31, for example in contact with the main conduit, so that the passage of gases in the bypass conduit 33 can, by heat exchange, participate in the rise in temperature of the main conduit 31 and consequently of the gas probe 2 installed in the main duct 31

The control member implements a control method for controlling the set of valves 36, 37.

This control method implements measurement steps, carried out repeatedly.

First of all, the method implements a step of acquiring the temperature of the gases in the vicinity of the gas inlet 30.

To this end, the device comprises a member for measuring the temperature in the vicinity of the entry of the gases 30 into the main duct 31.

The method also includes a step of acquiring the temperature of the gas probe. To this end, the device also includes a member for measuring the temperature of the gas probe.

The method then includes a step of detecting the start of the internal combustion engine.

When the engine is detected to be started, the method implements a temperature rise step of the gas probe.

This temperature rise is regulated according to the technical specifications of the gas probe used, up to its optimal operating temperature.

The method then proceeds to a step of controlling the valve in which

- When the temperature of the gases is higher than a dew point temperature, the set of valves 36, 37 is positioned in its first position, authorizing the passage of the gases in the main duct 31 and preventing the passage of the gases in the bypass duct 33 .

- When the temperature of the gases is lower than the dew point temperature, the set of valves 36, 37 is positioned in a second position preventing the passage of gases in the main conduit 31 and authorizing the passage of gases in the bypass conduit 33.

The dew temperature, also called the dew point, is the lowest temperature to which gases can be subjected without the formation of liquid water by saturation.

This dew point temperature is defined as a function of the nature of the gases entering the exhaust circuit, and can be modeled in particular when the engine operating point is operating.

Also when the dew temperature is reached, it is ensured that no drop of liquid water can come to settle on the gas probe, which is a risk of damage to the probe.

Also, by this control method, with reference to FIG. 4, it is possible to start the heating of the gas probe 42, as soon as the engine of the motor vehicle is started, without waiting for the gas temperature to reach the dew point 41, because the gases of which derivatives in the bypass conduit 33.

Also, the time for the gas probe to start operating, and consequently for the depollution, corresponds to the longest time between the dew point time 41 and the temperature rise time 42 of the gas probe 2, whereas in the prior art, the start-up time corresponded to the sum of these two durations 20, 21.

ίο Thus, one can improve in a relatively simple way the operation of an exhaust line of a motor vehicle, in particular by reducing the duration of operation of the depollution devices.

Claims (6)

1. A device for cleaning up exhaust gases from an internal combustion engine of a motor vehicle, said device comprising a circuit for exhausting gases from the combustion of said combustion engine, comprising a main exhaust duct ( 31) extending between a gas inlet (30) and a gas outlet (32), the device comprising at least one polluting gas probe (2) installed in said main gas exhaust duct (31), characterized in that the exhaust circuit further comprises a bypass duct (33) between an upstream bypass point (34) of the exhaust circuit, upstream of said gas probe (2), and a downstream bypass point (35) of the exhaust circuit, downstream of said gas probe (2); said exhaust circuit comprising in the vicinity of the upstream bypass point (34) a set of valves (36, 37) adapted to, in a first position, allow the passage of gases in the main duct (31) and prohibit the passage of gas in the bypass duct (33) and, in a second position, prohibit the passage of gases in the main duct (31) and allow the passage of gases in the bypass duct (33). 2. Device according to claim 1, characterized in that the set of valves (36, 37) comprises a first valve (36) installed in the main duct (31), downstream of said upstream branch point (34) and in upstream of the gas probe (2), and a second valve (37) in the bypass duct (33). 3. Device according to claim 1 or 2, characterized in that the bypass duct (33) extends in the vicinity of the main duct (31) so that, in the second position of the set of valves (36, 37 ), the gases passing through the bypass duct (33) produce a heating of the bypass duct (33) capable of heating the main duct (31) in the vicinity of the gas probe (2) by thermal conduction. 4. Method for controlling a pollution control device according to any one of claims 1 to 3, characterized in that it comprises repetitively - A step of acquiring the gas temperature in the vicinity of the gas inlet (30); - a step of acquiring the temperature of the gas probe (2); and in that it includes: - a step of raising the temperature of the gas probe (2); and a step of controlling said set of valves (36, 37) so that: o when the temperature of the gases is higher than a dew point temperature the set of valves (36, 37) is positioned in its first position, authorizing the passage of the gases in the main duct (31) and preventing the passage of the gases in the bypass duct (33); and o when the temperature of the gases is lower than the dew point temperature, the set of valves (36, 37) is positioned in a second position preventing the passage of gases in the main duct (31) and authorizing the passage of gases in the bypass duct (33). 5. Control member of a pollution control device according to any one of claims 1 to 3, adapted to implement the control method according to claim 4. 6. Engine assembly comprising an internal combustion engine, a pollution control device according to any one of claims 1 to 3 and a control member according to claim 5.