TECHNICAL FIELD

The present invention relates to an optimized process for cooling a SCR dozer for a catalytic exhaust of an automotive vehicle. BACKGROUND OF THE INVENTION

It is known that a catalytic exhaust comprises a selective catalytic reduction (SCR) dozer or metering module that controls injection of urea to transform oxides of nitrogen, called NOx, into water vapor and harmless nitrogen.

When the thermal engine of the vehicle is on, a mechanical pump driven by the thermal engine ensures the flowing of a coolant to cool the SCR dozer. However, the mechanical pump cannot be activated when the engine is off, which would lead to an increase of the catalytic exhaust after shutting off of the vehicle. In particular, an increase of the SCR dozer temperature could provoke damage of the dozer and urea sticking issue. To remedy this problem, it is known to use an additional dedicated electrical water pump to cool the SCR dozer when the engine is off, which unfortunately implies additional pipes, electronics and diagnosis and increases the cost of the catalytic exhaust and its maintenance. SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above- mentioned problem in providing a process for cooling a selective catalytic reduction (SCR) dozer for a catalytic exhaust of an automotive vehicle catalytic exhaust of an automotive vehicle, said process comprising, after an engine shut off, at least a phase, called purging-filling cycle, comprising the steps of purging an aqueous urea solution out of the SCR dozer, and filling the SCR dozer with the aqueous urea solution.

Thanks to the claimed process, when the engine is off, the SCR dozer is cooled by the urea that is renewed and hence maintained fresh during the purging- filling cycle. Consequently, no additional pump is needed, which reduces the cost of the catalytic exhaust as well as its maintenance.

The process may comprise a plurality of sequences of a purging-filling cycle and a thermal exchange phase.

A number of sequences may be comprised between 10 and 50, preferably between 15 and 30.

Each sequence of purging-filling cycle and thermal exchange phase may be activated when the dozer temperature is higher than a threshold.

The final purging step may be activated when the temperature reaches a second threshold, said second threshold being lower than the first threshold.

The thermal exchange phase may have a duration comprised between 20 seconds and 2 minutes, preferably 30 seconds.

The sequences of purging-filling cycle and thermal exchange phase may have a duration comprised between 5 minutes and 35 minutes.

During the purging step, a pump may be disposed in a tank of the aqueous urea solution generates a flow of the aqueous urea solution from the SCR dozer to the tank.

During the filling step, the pump may generate a flow of the aqueous urea solution from the tank to the SCR dozer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 is a schematic view of a device for carrying out a process for cooling a catalytic exhaust of an automotive vehicle as per the present invention in a purging step of the process.

Figure 2 is a schematic view of the device of figure 1 in a filling step of the process.

Figure 3 is a chronogram of the process as per the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is about a process P for cooling a selective catalytic reduction (SCR) dozer for a catalytic exhaust of an automotive vehicle. The process P is carried out by a device 10 illustrated in figures 1 and 2.

As shown in these figures, the device 10 comprises a tank 12 for storing an aqueous urea solution 14. The tank 12 is arranged to store between 15 litres to 20 litres of aqueous urea solution. The tank 12 is arranged in the vehicle such that the temperature of the stored aqueous urea solution 14 is of the same order as the ambient temperature, which should be around 30°C at the most.

The aqueous urea solution, sometimes sold under the brand “Adblue ®”, comprising a mixture of urea and demineralized water. The device 1 also comprises a selective catalytic reduction (SCR) dozer

16 and a pipe 18 connected to both the tank 12 and the SCR dozer 16. The SCR dozer is also known as metering module. The quantity of aqueous urea solution disposed in the SCR dozer 16 and the pipe 18 is around 2-3 grams.

The device 1 further comprises a pump 20 arranged inside the tank 12 and configured to make the aqueous urea solution flows from the SCR dozer 16 to the tank 12 (figure 1) via the pipe 18 and from the tank 12 to the SCR dozer (figure 2) via the pipe 18.

The SCR dozer 16 is connected to a catalytic exhaust body 22 such that the aqueous urea solution makes it possible to transform oxides of nitrogen, called NOx into water vapor and harmless nitrogen.

As can be seen from figures 1 and 2, a coolant 24 circulates in pipes to cool the catalytic exhaust 22. The flowing of the coolant 24 is generated by a mechanical pump (not illustrated) driven by the thermal engine of the vehicle.

The process P is now detailed. The process P takes place when the thermal engine of the vehicle is shut off. When the vehicle is off, the coolant 24 does not circulate since the mechanical pump is also stopped and the temperature of the catalytic exhaust increases. The process P ensures the cooling of the catalytic exhaust.

The process P comprises at least a first phase, called purging-filling cycle C, comprising the steps of:

- purging (PURG) the aqueous urea solution out of the SCR dozer, as illustrated in figures 1 and 3, and - filling (FIL) the SCR dozer with the aqueous urea solution, as illustrated in figures 2 and 3.

During purging, the pump 20 generates the flowing of the aqueous urea solution 14 from the SCR dozer 16 to the tank 12 through the pipe 18.

The SCR dozer is open during the purging step to allow the aqueous urea solution removal.

The purging step is performed during a given time (as described later) in order to only pump the quantity of aqueous urea solution present in the pipe 18 and dozer 16.

The purging step ensures the removal of all the aqueous urea solution 14 inside the SCR dozer and whose temperature is hot because of the increasing temperature of the catalytic exhaust.

As soon as the hot aqueous urea solution 14 penetrates the tank 12, its temperature decreases to reach the ambient temperature almost instantaneously.

Once all the hot aqueous solution has been removed from the SCR dozer 16 and the pipe 18, the pump speed is inverted to refill the SCR dozer 16 and the pipe 18 with fresh aqueous urea solution 14 in the filling step FIL.

During filling, the pump 20 generates the flowing of the aqueous urea solution 14 from the tank 12 to the SCR dozer 16 through the pipe 18. The SCR dozer is open during the filling step to allow air bubbles to be removed.

The purging-filling cycle C advantageously lasts a few seconds, between 0.5 seconds to 5 seconds, preferably 1 second or 2 seconds.

Once the purging-filling cycle C is finished, another phase of the process P takes place. This subsequent phase is a thermal exchanges phase ThP, wherein the aqueous urea solution 14 disposed inside the SCR dozer 16 exchanges calories such that the catalytic exhaust temperature reduces drastically.

The ThP phase lasts a time between 20 seconds and 2 minutes, preferably 30 seconds, as will be detailed later.

As shown in figure 3, the process P comprises a plurality of sequences of purging-filling cycle C and thermal phase ThP. The process P stops when the temperature of the SCR dozer 16 is below a temperature threshold, preferably 100°C, which corresponds to a duration comprised between 5 minutes and 35 minutes, preferably 10 minutes or 30 minutes. The final step of the process P is a purging step, such that no urea is left in the dozer.

As can be seen from figure 3, the process P is activated when the temperature of the dozer is higher than a threshold (of 140°C on figure 3). Then, thanks to the purging-filling cycle and the thermal exchange phase, the temperature decreases before increasing again until the threshold is reached again. When the lower threshold is reached, the purging-filling cycle is activated again, followed by another thermal exchange phase.

As can be seen from figure 3, after a given number of cycles, between 2 and 100, advantageously between 15 to 30, preferably around 20, the temperature of the dozer decreases until another lower threshold (of 110°C) is reached.

Then, the final purging is activated, the dozer being cooled sufficiently.

LIST OF REFERENCES

P cooling process

C purging-filling cycle

PURG purging step FIL filling step

ThP thermal phase

10 device for carrying out the process P

12 tank

14 aqueous urea solution

16 selective catalytic reduction (SCR) dozer 18 pipe

20 pump

22 catalytic exhaust body

24 coolant