SE528878C2 - Arrangement and method for recirculating exhaust gases of an internal combustion engine - Google Patents

Abstract

The present invention relates to an arrangement and a method for recirculation of exhaust gases of a combustion engine (1). The arrangement comprises a valve device (V1, V2) arranged in the return line (9) upstream from the EGR cooler (11) with respect to the intended direction of exhaust gas flow in the return line (9), and a control unit (10) which in certain situations is adapted to placing the valve device (V1, V2) in a cleaning position in which a portion of the return line (9b) which comprises the EGR cooler (11) is connected to surrounding air (13) so that compressed air from the inlet line (6) flows through said portion of the return line (9b) and the EGR cooler (11) before it is led out to surrounding air (13) by means of the valve device (V1, V2).

Description

528 878 _ at the same time as the flow resistance of the exhaust gases through the EGR cooler increases. Insufficient cooling of the exhaust gases leads i.a. to a deteriorating rnotorprestaiida.

WO 2004/067945 discloses an arrangement for exhaust gas recirculation of a supercharged dry combustion engine. The arrangement may, at certain times, provide a rearwardly directed air stream through the EGR cooler to clean it of soot coatings. However, such a rearwardly directed air pipe can only be provided at times when the pressure of the exhaust gases is lower than the pressure of the compressed air in an inlet line. This pressure difference is also often relatively limited so that a relatively small air gap is created, which is not sufficient to clean the EGR cooler efficiently.

SUMMARY OF THE INVENTION The object of the present invention is to provide an arrangement and a method of the kind mentioned in the introduction where the inner surfaces of the radiator are kept substantially free from soot coatings from the exhaust gases in an efficient and simple manner.

This object is achieved with the arrangement of the kind mentioned in the introduction, which is characterized by the features stated in the characterizing part of claim 1. Since the compressed air in the inlet line has a relatively large overpressure in relation to the ambient pressure, it is possible to create a strong flow of air from the inlet line, via the EGR cooler, to the surroundings, when the valve device is set in the cleaning position.

Since the passages of the EGR cooler are dimensioned to conduct and cool a relatively small amount of exhaust gases, such a strong air flow provides an intense load on the interior surfaces of the EGR cooler so that they are effectively cleaned of soot coatings.

According to a preferred embodiment of the present invention, the valve device comprises a first valve means which is arranged to control the flow of exhaust gases from the exhaust line to the return line. Such a first valve means may be a two-way valve of any kind. Advantageously, the first valve means is a damper which is adjustable in an open position when it allows exhaust gases from the exhaust line to pass through the return line and in a closed position when it prevents exhaust gases from passing through the return line. Such a damper can also be set in partially open positions so that the amount of returned exhaust gases through the return line can be controlled. The first valve means may be a conventional EGR valve. According to another preferred embodiment of the present invention, the valve device comprises a second valve means located downstream of the first valve means with respect to the intended flow direction of the exhaust gases in the return line, the control unit being arranged to set the second valve means in an open position so that it connects said part of the return line comprising the EGR cooler to ambient air when the valve device is in a cleaning position. Such a second valve means can be arranged directly in connection with the first valve means so that the valve means are included in a continuous valve device. Alternatively, a separate second valve means may be provided at a suitable location in the return line between the first valve means and the EGR cooler. The second valve means may be a two-way valve of any kind.

According to another preferred embodiment of the present invention, the control unit is arranged to set the valve device in the cleaning position at least at certain times during operation of the combustion engine when no exhaust gases are returned through the return line and when the combustion engine does not require substantially any supply of air. Since the cleaning of the EGR cooler does not normally need to be carried out immediately, it is advisable to carry it out on occasion so that the cleaning does not significantly affect the normal operation of the internal combustion engine and emissions of emissions. One such occasion is when the return line during operation is not used to return exhaust gases, ie. when the first valve means is in a closed position. The first valve member closes normally during the stages when the load of the internal combustion engine increases rapidly or decreases rapidly. During normal operation of a vehicle, rapid increases and decreases in the load of the internal combustion engine occur relatively frequently. There are therefore plenty of possible opportunities to clean the EGR cooler without affecting the recirculation of exhaust gases. In order not to interfere with the operation of the internal combustion engine, it is advisable to carry out the cleaning of the EGR cooler at times when the internal combustion engine does not essentially require any air supply. Such occasions occur in connection with the shifting of the vehicle when the driver releases the accelerator pedal. Although these occasions are relatively short-lived, they have a sufficient duration to be able to produce an air stream that blows the EGR cooler clean.

According to a preferred embodiment of the present invention, the arrangement comprises a sensor which is arranged to sense a parameter which is related to the degree of coatings in the EGR cooler and to inform the control unit of the value of said parameter. Such a sensor can be a pressure sensor with which it is possible to determine the pressure drop of the exhaust gases in the EGR cooler. The pressure drop of the exhaust gases in the EGR cooler is a parameter that increases with the degree of soot deposits in the EGR cooler. An alternative sensor 528 878 can be a fate meter that measures the exhaust fate through the EGR cooler. Exhaust emissions are a parameter that decreases with the degree of soot deposits in the EGR cooler. Advantageously, the control unit is arranged to set the valve device in a cleaning position after it has received values regarding said parameters which indicate that the degree of coatings in the EGR cooler exceeds a maximum acceptable value. Alternatively, the control unit can initiate. a cleaning process of the EGR cooler with substantially fixed time interval increments during operation of the internal combustion engine.

The above object is also achieved with the method of the kind mentioned in the introduction, which is characterized by the features stated in the characterizing part of claim 8.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, exemplary preferred embodiments of the invention are described with reference to the accompanying drawings, in which: Figs. Fig. 1 shows an arrangement for recirculating exhaust gases of a supercharged internal combustion engine according to a first embodiment, Fig. 2 shows an arrangement for recirculating exhaust gases of a supercharged internal combustion engine according to a second embodiment and Figs. 3 shows a fate diagram describing a method according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 shows an arrangement for recirculating a portion of the exhaust gases of a supercharged internal combustion engine 1, which may be a diesel engine or an otto engine. Such a recirculation is usually called EGR (Exhaust Gas Recirculation). The internal combustion engine 1 is advantageously intended as a drive engine for a heavier vehicle. Exhaust gases from the cylinders of the internal combustion engine 1 are led, via exhaust gas collector 2, to an exhaust line 3. The gases in the exhaust line 3, which have an overpressure, are led through a turbine 4. The turbine 4 thereby receives a driving force which is transmitted via a connection to a compressor 5 The compressor in 5 thereby compresses air which, via an inlet line 6, is led to the combustion engine 1.

The inlet line 6 comprises a charge air cooler 7 for cooling the compressed air before it is led via a branch 8 to the respective cylinders of the internal combustion engine 1. A return line 9 has the task of recirculating a part of the exhaust gases from the exhaust line 15 528 878 03. The return line 9 comprises a valve device which consists of a first valve means v; and a second valve member V2. An electric control unit 10 is arranged to set the valve means v ;, v; in desired positions during operation of the internal combustion engine 1. The control unit 10 may be a computer unit provided with a software stored on a data carrier 10a.

The return line 9 comprises an EGR cooler 11 for cooling the recirculating exhaust gases and an EGR mixer 12 by means of which the recirculating exhaust gases are mixed with the compressed air in the inlet line 6. The control unit 10 is intended to receive operation-related information 14 regarding the internal combustion engine 1 for control the valve means v ;, v; during operation.

The first valve means v; is here exemplified as a damper as adjustable in an open position when exhaust gases are to be returned through the return line 9 from the exhaust line 3 to the inlet line 6 and in a closed position when no exhaust gases are to be returned. The first valve member v; divides the return line 9 into a first part 9a which is located upstream of the valve means v; with respect to the intended flow direction of the exhaust gases in the return line 9 and a second part 9b which is located downstream of the valve means v ;. The first verrtilorganet v; has a construction so that it is possible to steplessly control its degree of opening so that a desired amount of exhaust gases can be returned through the return line 9. The first valve means v; may be a conventional EGR valve. The second valve member v; is arranged in the second part of the return line 9b in a position upstream of the charge air cooler 11 with respect to the intended flow direction of the exhaust gases in the return line 9. The second valve means v; is normally kept in a closed position during operation of the internal combustion engine 1. When the second valve member v; placed in an open position, the second part of the return line 9b is connected to ambient air 13.

During operation of the vehicle, the control unit 10 receives substantially continuously operation-related information 14 regarding the internal combustion engine 1. With information about, for example, the fuel supply to the internal combustion engine 1, the control unit 10 can determine the load of the internal combustion engine. The information also includes information on the engine operating speed n and other parameters required to control the amount of exhaust gases to be recirculated. When the internal combustion engine 1 is driven with a substantially constant load, the control unit 10 more or less holds the first valve member v; in an open position so that a suitable amount of exhaust gases from the exhaust line 3 is led through the return line 9 and mixed with the compressed air in the inlet line 6. During, for example, rapid changes in the load of the internal combustion engine, the control unit 10 closes the first valve means v; and thus stops the recirculation of exhaust gases to the internal combustion engine 1. The control unit 10 closes the first valve member vi during operating times when a rapidly rising load is required by the internal combustion engine to increase the proportion of clean air which. via the inlet line 6. led to the internal combustion engine l.

The internal combustion engine 1 is thus quickly obtained an increased load without the amount of emissions increasing. The control unit 10 closes the first valve means v; even during operating times when the internal combustion engine receives a rapidly reduced load in order to maintain the charge pressure of the air as long as possible, which can be used in a later rapid increase in the engine load. A rapidly reduced load is obtained. for example, during a changeover process in the vehicle when a driver of the vehicle releases the accelerator pedal.

However, the exhaust gases passed through the return line 9 contain soot particles which, during the passage through the EGR cooler II, risk being deposited on the heat-transferred surfaces of the EGR cooler II so that soot deposits form. Soot deposits on the EGR radiator's 1 l heat transfer surfaces impair the radiator's ability to cool the exhaust gases. Insufficient cooling of the exhaust gases leads i.a. to a deterioration of engine performance. Soot coatings block the flow passages of the exhaust gases through the EGR cooler 1 l. This reduces the exhaust flow through the return line 9, which can lead to an increased emission of emissions from the internal combustion engine l.

When the control unit 1 has received operation-related information 14 indicating a rapidly reduced load or a rapidly increasing load, the control unit 10 places the first valve means V1 in a closed position so that no exhaust gases are returned through the return line 9. Thus, there is a possibility to set the second valve means v; in an open position. In the open position, the second valve means vg connects the second part 9b of the return line with ambient air 13. When the first valve means V1 is in a closed position and the second valve means v; in an open position, the valve device is set in a cleaning position. In the cleaning mode, a strong flow of air is provided from the inlet line 6 through the second part of the return line 9b and the EGR cooler 11 and out to the environment 13 via the second valve means v2. The rapid air flow is initiated by the large pressure difference that exists between the compressed air in the inlet duct 6 and ambient air 13. The return duct 9 is dimensioned to conduct a considerably smaller amount of exhaust gases than the amount of compressed air which in this case flows through the second part. of the return line 9b and the EGR cooler 1 l. This flow of clean air flowing at a high speed through the EGR cooler l 1 in a direction opposite to that which exists when exhaust gases are recirculated cleans its internal surfaces from soot 528 878 coatings. The control unit 10 has the possibility of setting the second valve member vg in an open position each time the first valve member V1 is in a closed position. However, in order not to affect the operation of the internal combustion engine 1, it is suitable to place the second valve member V2 in an open position only during occasions when the internal combustion engine 1 does not substantially require any air supply. Such an opportunity occurs i.a. in connection with a gear change process in the vehicle immediately before a gear is switched off. During this relatively short time, the second valve member v; is opened so that a rapid cleaning air flow through the EGR cooler 1 1 is obtained. The guide unit 10 can set the second valve member v; in an open position at any time as the first valve means we are in the closed position and the internal combustion engine 1 does not require any air supply. In many cases, however, it is not justified to clean the EGR cooler 1 I at each such operating time, but the control unit may be pre-programmed to start the cleaning after a certain number of times, for example, every tenth such operating time occurs or after a predetermined time. for fl utit since the last cleaning.

Pig. 2 shows an arrangement which corresponds to the arrangement described above but which is also supplemented with a pressure sensor 15 which is arranged in the second part of the return line 9b downstream of the EGR cooler 1 1. The pressure sensor 15 has the task of sensing the exhaust gases after they have left The EGR cooler 11. The pressure sensor 15 is arranged to send a signal to the control unit 10 regarding measured pressure values. The control unit 10 is assumed to have knowledge of the exhaust gas pressure in the exhaust line 3 or the like so that the exhaust gas pressure drop through the EGR cooler 11 can be determined. The pressure drop of the exhaust gases is in relation to the degree of soot deposits in the EGR cooler's 11 flow channels. The control unit 10 can here iron estimate values of the exhaust gas pressure drop when they have passed through the EGR cooler 11 with a reference value. When the estimated pressure drop exceeds the reference value, it is time to clean the EGR cooler 1 1. Here the control unit 10 can set the second valve means v; in the open position as soon as an operating condition arises when the first valve means we are in the closed position and the internal combustion engine 1 does not require any air supply. This results in a short-term strong air flow through the return line 9 and the EGR cooler 11, which effectively cleans their internal surfaces from soot coatings. The soot coating nits are blown out to ambient air 13 or collected in a filter or the like which is mounted in connection with the outlet of the second valve member.

Fig. 3 shows a flow chart describing a method for controlling exhaust gas recirculation. The process started at 16. At 17, the control unit 10 receives operation-related in- '15 m 9% 528 878 formation 14 and decides whether exhaust gases are to be returned through the return line 9 or not.

If the internal combustion engine 1, for example, receives information 14 indicating a substantially constant load on the internal combustion engine, the control unit 10 finds that there is no obstacle to recirculating exhaust gases through the return line 9. In this case, the control unit 10 sets at 18, the first valve means V1 in an open position and the second valve member v; in a closed position. If the control unit 10 receives information in a sanitary manner, for example from the pressure sensor 15 which indicates that the EGR cooler 11 has to wait until a later more suitable occasion when a process in which a EGR cooler 11 is usually not so urgent that it needs to be rectified immediately . Then the process restarts at 16.

If the control unit 10 instead receives information 14 which indicates a rapidly increasing or decreasing load of the internal combustion engine 1, it states that the recirculation of exhaust gases through the return line 9 must be stopped. At 19, the control unit 10 places the first valve member V1 in a closed position. Then the control unit decides, at 20, whether the EGR cooler 11 needs to be cleaned. The control unit 10 can make such a decision with the aid of information from the pressure sensor 15 or with knowledge of when the last cleaning was performed. If no cleaning needs to be performed, the control unit 10, at 21, keeps the second valve member V2 in a closed position. Then the process restarts at 16. If the control unit 10 instead finds that a cleaning of the EGR cooler 11 needs to be performed, the second valve means v is set; in an open position at 22. Thus, the compressed air in the inlet line 6 is connected to air 13 of ambient pressure. The pressure difference between the compressed air in the inlet line 6 and it. ambient air 13 results in a relatively large air velocity at a high velocity passing through the second part of the return line 9b and the EGR cooler 11 so that its inner surfaces are cleaned of soot coatings. With such regular cleaning processes during operation, the internal combustion engine 1 can maintain a stable performance for a long period of operation without the need for service work to clean the EGR cooler 11.

Of course, all of the process steps, as well as arbitrary sub-sequences of steps, described above can be controlled by a computer program which is directly loadable to the internal memory of a computer, and includes suitable software for controlling the necessary steps when the program is run on the computer. In addition, although the embodiment of the invention described with reference to the software is controlled by a computer and processes performed by a computer, the invention also extends to computer programs, especially those computer programs which are stored on a data carrier adapted to realize 528 878 invention. The program may be in the form of source code, object code, a code which consists of a level between source and object code, for example in partially compiled form, or in any other form suitable for use in implementing the method according to the invention. The data carrier can be any entity or device which is capable of storing the program. For example, the data carrier may include storage media, such as ROM (Read Only Memory), PROM (Programmable read-only meniory).

EPROM (Erasable PROM), Flash or EEPROM (Electrically EPROM). In addition, the data carrier may be a transmissible carrier, such as an electrical or an optical signal which may be transmitted via an electrical or optical cable or by radio or otherwise. When the program is included in a signal which can be conducted directly through a cable or other device or means, the data carrier can be constituted by such a cable, device or equipment. Altematixft, the data carrier can be an integrated circuit in which the program is stored, where the integrated circuit is adapted to perform, or used in performing relevant processes.

The invention is in no way limited to the embodiment described in the drawing but can be varied freely within the scope of the claims. The pressure sensor shown in Fig. 2 can be replaced by another sensor that senses a parameter that is related to the degree of soot coatings in the EGR cooler. The valve device need not comprise two separate valve means V1, v; but it may consist of a uniform valve of any kind having a corresponding function. The invention is applicable to essentially all types of dry combustion engines where air is supplied with an overpressure to the internal combustion engine.

Claims (16)

10 15 20 25 30 35 528 878 10 Patent claims An arrangement for recirculating exhaust gases of a supercharged combustion engine (1), the arrangement comprising an inlet conduit (6) arranged to direct compressed air to the combustion engine (1), a return conduit (9) arranged to recirculate exhaust gases from a combustion engine. . exhaust line (3) of the combustion atom (1) to a connection point (12) with the inlet line (6) and an EGR cooler (1 1) arranged in the return line (9) for cooling the exhaust gases, characterized in that the arrangement comprises a valve device (V1, V2) arranged in the return line (9) upstream of the EGR cooler (1 1) with respect to the intended direction of flow of the exhaust gases in the return line (9) and a control unit (10) which, in certain cases, is arranged to place the valve device (V1, V2) in a cleaning position in which position the valve device (vi, V3) connects a part of the return line (9b) which comprises the EGR cooler (1 l) to ambient air (13) so that compressed air from the inlet line (6) flows through said part of the return line (9b) and the EGR cooler (1 l) before it is led out to ambient air (13). Arrangement according to claims 1, characterized in that the valve device comprises a first valve means (V1) which is arranged to control the flow of exhaust gases from the exhaust line (3) to the return line (9). Arrangement according to claim 2, characterized in that the first valve means (Vi) comprises a damper which is adjustable in an open position when it allows exhaust gases from the exhaust line (3) to pass through the return line (9) and in a closed position when it prevents exhaust gases from passing through the return line (9). Arrangement according to claim 2 or 3, characterized in that the valve device comprises a second valve means (V2) which is located downstream of the first valve means (v;) with respect to the intended flow direction of the exhaust gases in the return line (9). wherein the control unit (10) is arranged to place the second valve means (V2) in an open position so that it connects said part of the return line (9b) which comprises the EGR cooler (11) with ambient air (13) when the valve device (vi , V2) is in a cleaning mode. Arrangement according to one of the preceding claims, characterized in that the control unit (_10) is arranged to set the valve device (vi, V2) in the cleaning position at least at certain times during operation of the internal combustion engine (1) when no exhaust gases are returned through the control unit. 52 35 528 878 11 the return line (9) and since the internal combustion engine (1) does not require substantially any supply of air. Arrangement any of the preceding claims. characterized in that the arrangement comprises a sensor (15) arranged to sense a parameter related to the degree of occupancy in the EGR cooler (11) and to inform the control unit (10) of the value of said parameter. Arrangement according to claim 6, characterized in that the control unit (10) is arranged to set the valve means (vi, V2) in a cleaning position after it has received values regarding said parameters which indicate that the degree of coatings in the EGR cooler (11) exceeds a maximum acceptable value. A method for recirculating exhaust gases of an overcharged combustion engine (1), the method comprising the steps of directing compressed air to the internal combustion engine via an inlet line (6), recirculating exhaust gases from an exhaust line (3) of the internal combustion engine. (1) Via a return line (9) to a dry connection point (12) with the inlet line and to cool the exhaust gases in the return line (9) in an EGR cooler (11). lg; drawn by the steps of arranging a valve device (V1, V2) in the return line (9) upstream of the EGR cooler (1 1) with respect to the intended direction of flow of the exhaust gases in the return line (9) in the inlet line (6), and at certain times setting the valve device (V1, V2) in a cleaning position in which position the valve device (v1, V2) connects a part of the return line (9b) comprising the EGR cooler (1 1) to ambient air (13) so that compressed air from the inlet line (6) flows through said part of the return line (9b) and the EGR cooler (1 1) before it is led out to ambient air (13). Method according to claim 8, characterized by the steps of controlling the flow of exhaust gases' from the exhaust line (3) to the return line (9) by means of a first valve means (vi). Method according to claim 9, characterized by the steps of controlling the flow of exhaust gases from the exhaust line (3) to the return line (9) by means of a damper (vi) which is adjustable in an open position as it allows exhaust gases from the exhaust line (3) to pass through the return line (9), and in a closed position as it prevents exhaust gases from passing through the return line (9). 10 15 20 25 528 878 12 Method according to claim 9 or 10, characterized by the step of placing a second valve means (V2), which is located downstream of the first valve means (vi) with respect to the intended direction of flow of the exhaust gases in the return line (9), in an open position so that it connects said part of the return line (9b) which comprises the EGR cooler (11) to ambient air (13) when the valve device (vi, vg) is in a cleaning position. Method according to one of the preceding claims 8 to 11, characterized by the step of placing the valve device (vi, vz) in the cleaning position at least at certain times during operation of the internal combustion engine (1) when no exhaust gases are returned through the return line (9) and when the internal combustion engine (1 ) essentially does not require any supply of air. Method according to any one of the preceding claims 8 - 2, characterized by the step of sensing a parameter related to the degree of coatings in the EGR cooler (11) and informing the control unit (10) of the value of said parameter. Method according to claim 13, characterized by the step of setting the valve device (vi, V2) to the cleaning position after values have been sensed with respect to said parameters which indicate that the degree of coatings in the EGR cooler (l 1) exceeds a maximum acceptable value. 15., 15. A computer program, directly loadable to the internal memory of a computer. comprising injecting software for controlling the method, according to any one of claims 8 to 14 when the program is run on a computer. A computer readable medium (10a) on which a program is stored, which is adapted to cause a computer to control the method according to any one of claims 8 to 14.