AIXALA, Luc (4 Rue de la Loge, Lyon, Lyon, F-69005, FR)
| CLAIMS
1. An exhaust gas recirculation system (2) for an internal combustion engine (1), said system comprising an exhaust gas cooler (27), characterized in that said system includes a source (3) of fresh air under pressure and a fresh air injection line (29) connecting said source to said cooler.
2. System according to claim 1 characterized in that a check valve (291 ) incorporated into said air injection line (29) prevents gas flow (F) from said cooler
(27) to said source of air (3).
3. System according to one of claims 1 or 2 characterized in that a valve (292) incorporated into said air injection line (29) controls air flow (F) between said source of air (3) and said cooler (27).
4. System according to one of claims 1 to 3, characterized in that said source of air is a tank (3).
5. An internal combustion engine (1 ) equipped with an exhaust gas recirculation system (2) according to one of the previous claims.
6. An automotive vehicle (T) equipped with an engine (1 ) according to claim 4, said source (3) of fresh air under pressure forming a source of fresh air under pressure (A 3 ) for accessories or auxiliary equipments of said vehicle.
7. A method for cleaning an exhaust gas recirculation system (2) of an internal combustion engine (1 ), said system comprising an exhaust gas cooler (27), characterized in that it includes a step of injecting fresh air (F) under pressure into said cooler (27) when said engine is being turned off.
8. Method according to claim 7 characterized in that said fresh air injection step (F) takes every time said engine (1 ) is being turned off.
9. A method for cleaning an exhaust gas recirculation system (2) of an internal combustion engine (1 ), said system comprising an exhaust gas cooler (27), characterized in that it includes a step of injecting fresh air (F) under pressure into said cooler (27) when said engine is running.
10. Method according to one of claims 7 to 9 characterized in that, during said fresh air injection step (F), a valve (28), which controls the percentage of exhaust gas recirculation when said engine (1 ) runs, is set to a closed position. |
EXHAUST GAS RECIRCULATION SYSTEM AND METHOD FOR CLEANING
SUCH A SYSTEM
TECHNICAL FIELD OF THE INVENTION
This invention concerns an exhaust gas recirculation system for an internal combustion engine. It also concerns an internal combustion engine equipped with such a system and an automotive vehicle equipped with such an engine. Finally, the invention concerns a method for cleaning an exhaust gas re-circulation system.
BACKGROUND ART OF THE INVENTION
It is known, e.g. from US-B-6 659 090, to use exhaust gas recirculation means (EGR means) on an internal combustion engine to re-direct a part of the exhaust gases towards the cylinders of the engine in order to reduce NO x emissions and to comply with future anti-pollution regulations. Such EGR means generally include an exhaust gas cooler used to lower the temperature of the exhaust gases prior to sending them back to the engine. When the engine is stopped, the exhaust gases trapped in the EGR cooler cool down and some impurities present in these gases form a deposit or stains, e.g. a sulphur deposit, on the inside parts or walls of the cooler. Such a deposit or stain causes oxidation of the internal parts or walls of the cooler. This oxidation might result in defective working of the cooler. In particular, exhaust gases might come into contact with parts of the engine located in the vicinity of the cooler of even with the cooling medium circulating through the cooler.
SUMMARY OF THE INVENTION
The invention aims at providing an exhaust gas recirculation system whose gas cooler has a longer life-time. To this aim, the invention concerns an exhaust gas recirculation system for an internal combustion engine, this system comprising an exhaust gas cooler and being characterized in that it also includes a source of fresh air under pressure and a fresh air injection line connecting this source to this cooler.
Thanks to the connexion line, it is possible to inject into the exhaust gas cooler some fresh air provided by the source when the engine is being turned off.
This allows efficient cleaning of the inside volume of the cooler, so that sulphur deposits or other deposits or stains are avoided.
According to further aspects of the invention, an exhaust gas recirculation system might incorporate one or several of the following features : - A check valve incorporated into the air injection line prevents gas flow from the cooler to the source of air.
- A valve incorporated into the air injection line controls air flow between said source and said cooler.
- The source of air is a tank. The invention also concerns an internal combustion engine equipped with an exhaust gas recirculation system as mentioned here-above.
The invention also concerns an automotive vehicle, in particular a truck, equipped with an engine as mentioned here-above and where the source of fresh air under pressure also forms a source of fresh air under pressure for accessories or auxiliary equipments of the vehicle.
The invention also concerns a method for cleaning an exhaust gas recirculation system of an internal combustion engine, this system comprising an exhaust gas cooler. This method is characterized in that it includes a step of injecting fresh air under pressure into the cooler when the engine is being turned off. Advantageously, the injection of fresh air takes place every time that the engine is being turned off.
Another method according to the invention is characterized in that fresh air injection takes place when the engine is running.
Moreover, in both methods, during fresh air injection, a valve, which controls the percentage of exhaust gas recirculation when the engine runs, is advantageously set to a close position, which prevents fresh air injected into the cooler to flow towards the exhaust collector of the engine.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood on the basis of the following description, which is given in correspondence with the annexed figures and as an illustrative example, without restricting the object of the invention. In the annexed figures :
- figure 1 is a scheme of an internal combustion engine equipped with an exhaust gas recirculation system according to the invention, in a configuration where the engine runs.
- figure 2 is a scheme similar to figure 1 , when the engine is being turned off.
DETAILED DESCRIPTION OF ONE EMBODIMENT
The Diesel engine 1 represented on figure 1 is mounted onto a truck T and equipped with an exhaust gas recirculation system or "EGR" system. The EGR system 2 comprises a first line 21 which feeds an air inlet collector 11 of engine 1 with air to be used during fuel combustion in the cylinders 12 of engine 1 as shown by arrows A 1 .
Air in line 21 is brought to the pressure required to feed collector 11 by a compressor 22.
An air outlet collector 13 of motor 1 is connected to an exhaust line 23 in which a.turbine 24 sucks air from collector 13 as shown by arrows A 3 .
Compressor 22 and turbine 23 are connected by a rigid shaft 25 and belong to the same structural unit called "turbocompressor". A derivation line 26 connects line 23, upstream of turbine 24, to line 21 , downstream of compressor 22. An exhaust gas cooler 27 is mounted on line 26 and lowers the temperature of gases coming from line 23 and going to line 21.
Cooler 27 is a liquid/gas heat exchanger fed with a liquid cooling medium, as shown by arrow Li, this medium being evacuated from this cooler as shown by arrow l_ 2 . According to a further embodiment of the invention, cooler 27 can be a gas/gas heat exchanger. In such a case, the cooling medium is a gas. A proportional control valve 28 is mounted on line 26, upstream of cooler 27 and is used to control the percentage of exhaust gases directed to cooler 27 and line 21 , as shown by arrows R, with respect to the total quantity of exhaust gases circulating in exhaust line 23. For this purpose, control valve 28 is controlled by a signal Si provided by a non represented electronic control unit (ECU) of engine 1. On the truck T, a tank 3 is provided to store air under pressure, the pressure of this air being increased from atmospheric pressure to about 10 bars thanks to a compressor 4. Air of tank 3 is used to actuate or feed accessories or auxiliary equipments of the truck such as a braking assistance system, a pneumatic
suspension system or a tyre pressure control system, as represented by arrows A 31 , A32 and A 3 3-
A fresh air injection line 29 connects tank 3 to an upstream portion 261 of line 26 located between valve 28 and cooler 27. In other words, line 29 connects tank 3 to the volume of cooler 27 where exhaust gases circulate, as shown by arrow R on figure 1.
A check valve 291 is mounted on line 29 and prevents flow of exhaust gases from line 26 to line 29 and tank 3.
A control valve 292 is incorporated in line 29. It allows or blocks air flow in line 29, on the basis of a control signal S 2 received from the ECU.
When engine 1 runs, as represented on figure 1 , EGR system 2 provide collector 11 with a part of the exhaust gases flowing in line 23, the proportion of exhaust gases redirected to cooler 27 and line 21 , as shown by arrows R, being controlled by valve 28 piloted with signal S 1 . Signal S 2 pilots valve 291 to close line 29.
When the engine is turned off, signal Si pilots valve 28 to close the communication between line 23 and portion 261 of line 26. Then, control signal S 2 is applied to valve 292 to open the communication between tank 3 and portion 261 of line 26, which induces that a quantity of fresh air flows from tank 3 to line 21 through valve 292 line 29, check valve 291 , portion 261 , cooler 27 and the downstream portion 262 of line 26, as shown by arrows F.
Such a flow F of air cleans the inside volume of cooler 27 where exhaust gases circulate when engine 1 runs. This prevents depositions or stains of solid particles, like sulphur particles, which are blown away by the flow F of air coming from tank 3. This avoids oxidation of the internal parts or walls of cooler 27.
Flow of air F also cleans lines 26 and 21 , which also prevents deposits in these parts of EGR system 2.
Preferably, signal S 2 is applied to valve 292 every time that engine 1 is turned off, so that cleaning of cooler 27 and lines 21 to 26 takes place every time that engine 1 is turned off.
However, one can consider a method where cleaning of cooler 27 takes place in function of several parameters, e.g. a p re-determined number of hours of working of engine 1 since the last cleaning or the temperature of the engine.
Since cleaning of cooler 27 takes place when engine 1 is turned off, the pressure in tank 3 is high, in the order of 10 bars, because compressor 4 has just filled tank 3 during working of engine 1. This relatively high pressure of fresh air facilitates cleaning of cooler 27 since pressure in lines 26 to 21 is generally lower than 6 bars.
According to another approach, cleaning of cooler 27 can also take place when engine 1 is running since pressure in tank 3 is available as soon as the engine runs. In particular, cleaning can take place when the engine is running at idling speed or at partial load, or after a predetermined duration of operation. Control of the cleaning operation is made by an electronic control unit mounted onto truck T.
In this case also, during fresh air injection, valve 28 is set to a closed position.
Tank 3 and compressor 4 are equipments that are usually provided on a truck in order to feed accessories or auxiliary equipments, so that using the invention on a truck does not substantially increase its manufacturing cost since only line 29 and valves 291 and 292 have to be added with respect to most trucks equipped with an EGR system.
Valve 291 is optional and one can control the flow of air in line 29 with valve 292 only. Insofar as check-valve 291 is used, valve 292 can be omitted, in particular if tank 3 includes means to control air flow towards the outside of tank 3 or if independent means are provided to control compressor 4.
The invention has been represented with respect to a truck T whose engine is equipped with an EGR system. However, it can also be used for other automotive vehicles equipped with such a system. The engine equipped with the EGR system can be any kind of internal combustion engine.
LIST OF REFERENCES
1 engine
11 air inlet collector
12 cylinder
13 air outlet collector
2 EGR system
21 feeding line
22 compressor
23 exhaust line 24 turbine
25 shaft
26 derivation line
261 upstream portion
262 downstream portion 27 exhaust gas cooler
28 control valve
29 fresh air injection line
291 check valve
292 control valve
3 tank
4 compressor
Ai arrows (air flow)
A 3 arrows (air flow)
A 31 , A 32 , A 33 arrows (air flow from tank 3)
F flow of fresh air from tank 3 to cooler 27
Li arrow (cooling medium flow) l_ 2 arrow (cooling medium flow)
R arrow (exhaust gas re-circulation flow)
51 signal
52 signal T truck
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