SE528881C2 - 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 means (S<SUB>2</SUB>) arranged in the inlet line (6), a line (13) extending from the valve means (S<SUB>2</SUB>) to a connection point (9a) to the return line, which connection point (9a) is situated 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 means (S<SUB>2</SUB>) in a cleaning position so that at least part of the compressed air in the inlet line (6) is led via the valve means (S<SUB>2</SUB>) and said line (13) to the return line (9), whereby the air is led in such a direction that it flows through the EGR cooler (11).

Description

52 25 881 thereby increasing the flow resistance of the exhaust gases through the EGR cooler. Insufficient cooling of the exhaust gases leads i.a. to a deteriorating engine performance.

WO 2004/067945 discloses an arrangement for recirculating exhaust gases of a supercharged internal combustion engine. The event may, on certain occasions. provide a rearward flow of air through the EGR cooler to clean it from soot deposits. However, such a reverse air flow can only be achieved 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 enough 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 of 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. With such a valve member arranged in the inlet line, it is possible to direct the compressed air from the inlet line to the return line and further through the EGR cooler. Since the air flow in the inlet line is considerably larger than the normal exhaust flow through the return line, an air flow of a size and with a force through the EGR cooler is provided so that its inner surfaces are effectively cleaned of soot coatings.

Preferably, the valve means is set in a position so that it directs the entire air flow in the inlet line to the return line. This provides a maximum air flow and an optimal cleaning of the return line and the EGR cooler.

According to a preferred embodiment of the present invention, the return line comprises an EGR valve arranged to control the flow of exhaust gases from the exhaust line to the return line and that said line connection point with the return line is located downstream of the EGR valve but upstream of the EGR cooler with respect to the intended flow direction of the exhaust gases in the return line. Thus, with the EGR valve in a closed position, it is possible to control the air flow in the return line in one direction so that the entire air flow passes through the EGR cooler. Advantageously, the control unit is arranged to set the valve means in the cleaning position during the operating condition of the internal combustion engine when the EGR valve is closed. As no exhaust gases are led in the return line when the EGR valve is closed, it is obligatory to take care to clean the EGR cooler at such times. Thus, the cleaning of the EGR cooler does not result in any increases in the emissions from the internal combustion engine compared to a conventional operation. The EGR valve normally closes during the stages when the load on the 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 opportunities to clean the EGR cooler without affecting the exhaust gas recirculation process.

According to a preferred embodiment of the present invention, the arrangement comprises a sensor arranged to sense a parameter 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 can be a flow meter that measures the exhaust flow 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 means in a cleaning position at times when it has received values regarding said parameters which indicate that the degree of coatings in the EGR cooler exceeds a highest acceptable value. Alternatively, the control unit can initiate a cleaning process of the EGR cooler at fixed time intervals during operation of the combustion engine.

According to another preferred embodiment of the present invention, the control unit is arranged to receive information regarding the speed of the internal combustion engine and that the control unit is arranged to set the valve means in said purification position and the EGR valve in an open position if the internal combustion engine speed exceeds a maximum acceptable speed. By placing the valve member and the EGR valve in the above-mentioned positions, not enough air is led to the cylinders of the internal combustion engine for the fuel to ignite. The internal combustion engine provides an emergency stop and the risk of damage that can occur during an overheating of the engine is eliminated. Thereby an additional friction is provided with the valve means. 10 15 20 25 V30 las 528 881. According to another preferred embodiment of the present invention, the inlet line comprises a compressor which compresses the air in the inlet line and that the valve means is located downstream of the compressor with respect to the flow direction of the air in the inlet line. In order for compressed air to be able to be led through the EGR cooler, it is necessary for the valve means to be located downstream of the compressor. Advantageously, the inlet line comprises a charge air cooler and that the valve means is located upstream of the charge air cooler with respect to the air flow direction in the inlet line. This conducts hot compressed air at a high speed through the EGR cooler. Hot compressed air cleans the EGR cooler more efficiently than compressed air cooled in the charge air cooler.

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 9.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, exemplary preferred embodiments of the invention are described with reference to the accompanying drawings, in which: Fig. 1 shows an arrangement for recirculation of exhaust gases of a supercharged internal combustion engine according to a first embodiment, Fig. 2 shows the arrangement in Fig. 1 during cleaning of an EGR cooler, Fig. 3 shows the arrangement in Fig. 1 during an emergency stop of the internal combustion engine, Fig. 4 shows an arrangement for recirculation of exhaust gases of a supercharged internal combustion engine according to a second embodiment and Fig. 5 shows a fl fate diagram describing a method according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Figs. 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 combustion engine 1 are led, via exhaust collector 2, to an exhaust line 3. The exhaust 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 5 thereby compresses air which, via an inlet line 6, is led to the internal combustion engine 1. The inlet line 6 comprises a charge air cooler 7 for cooling the compressed air before it, via a branch 8, is led to the respective engines of the internal combustion engine 1. A return line 9 is intended to recirculate a part of the exhaust gases from the exhaust line 3. The return line 9 comprises an EGR valve in the form of a first adjustable damper s ;, with which the exhaust flow in the return line 9 can be switched off if necessary. To some extent, the first damper can s; also used to control the amount of exhaust gases passed through the return line 9. An electric control unit 10 is arranged to set the first damper s; in a desired position 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 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-transferring surfaces of the EGR cooler II so that soot deposits form. Soot coatings on the heat-transferring surfaces of the EGR cooler 11 impair the cooler's ability to cool the exhaust gases. Insufficient cooling of the exhaust gases leads i.a. to a deterioration of engine performance. Soot deposits also block the flow passages of the exhaust gases through the EGR cooler l 1. 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. A valve means in the form of a second damper s; is arranged in the inlet line 6 in a position between the compressor 5 and the charge air cooler 7. A line 13 extends between the second damper s; and a connection point 9a with the return line 9. The connection point 9a with the return line 9 is located between the first damper s; and the EGR cooler ll. The electric control unit 10 is arranged to receive operation-related information 14 regarding the dry combustion engine 1 in order to enable control of the first damper s; and other damper sz.

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 accelerator motor 1 is driven at a substantially constant load, the control unit 10 holds the first damper s; in an open position. Thus, a suitable amount of exhaust gases from the exhaust line 3 will be passed through the return line 9 and mixed with the compressed air in the inlet line 6. Under certain operating conditions, however, the control unit 10 closes the first damper s. This occurs, for example, during rapid changes in the load of the internal combustion engine. The control unit 10 closes the first damper s; under a rapidly increasing load to increase the proportion of pure lu fl which, via the inlet line 6, is led to the internal combustion engine 1. The increased load is thus achieved quickly without increasing the amount of emissions. The control unit 10 closes the first damper s; under 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, among other things, during a shifting process in the vehicle when a driver of the vehicle releases the accelerator pedal.

Fig. 1 shows the arrangement during a stage when the control unit 10 receives operation-related information 14 which indicates that the combustion engine is operated with a substantially constant load. The control unit 10 has set the first damper s; in an open position so that exhaust gases are returned from the exhaust line 3, via the return line 9, to the inlet line 6.

The control unit 10 has set the second damper s; in a normal position so that all compressed air compressed by the compressor 5 in the inlet line 6 is led by the second damper s; to the charge air cooler 7 before the air is mixed with the returning exhaust gases in the EGR mixer 12.

Fig. 2 shows the arrangement during a stage when the control unit 10 has received operation-related information 14 which indicates a rapidly reduced load. A driver of the vehicle may have released the accelerator pedal here to put a new gear in the vehicle's gearbox.

The control unit 10 here stops the recirculation of exhaust gases through the return line 9 by setting the first damper s; in a closed position. The control unit 10 now has the possibility of setting the second damper s; in a purification position so that compressed air from the compressor 5 is led to the return line 9. In the purification position the compressed air is led through the line 13 before it reaches the return line 9 at the connection point 9a between the first damper s; and the EGR cooler 7. Since the first damper s; is closed, the air can continue to flow only in one direction through the return line 9. The air then passes through the EGR cooler. The return line 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 return line 9 and the EGR cooler 7 This large flow of clean air, 10 15 m 25 30 35 528 881 flowing through the EGR cooler 11 at a high speed, effectively cleans the interior surfaces of the EGR cooler from soot deposits. The control unit 10 has the possibility of setting the second damper sz in a cleaning position each time the first damper s; is set to a closed position. The control unit 10 may be intended to set the second damper s; in a purification mode at predetermined intervals. The control unit 10 can set the second damper s; in a purification mode. for example, every ten times the first spiällct s. is placed in the closed position. The control unit 10 may also be arranged to set the second damper s; in a cleaning mode with fixed time intervals for cleaning the EGR cooler 1 1. When such a time interval has passed, the control unit 10 may on the next occasion as the first damper s; closes set the second damper s; in the purification mode. Alternatively, the control unit 10 can close the first damper S1 directly and set the second damper s; in a purification mode when such a time interval has passed independently of the load of the dry combustion engine.

Fig. 3 shows the arrangement during a stage when the Control Unit 10 has received information 14 regarding the speed n of the internal combustion engine 1 which indicates an uncontrolled acceleration of the internal combustion engine 1. Engine acceleration can be considered to exist when the engine speed n exceeds a maximum acceptable engine speed nmax. When the Control Unit 10 receives information indicating that the engine speed n exceeds the maximum acceptable engine speed nnmx, the Control Unit 10 sets the first damper s; in an open position and the other damper s; in a purification mode. Thus, the compressed air in the inlet line 6, via the second damper S2, is led to the return line 9. Since the first damper S1 and is in an open position, the air is led mainly in the direction of exhaust line 3. Thus, so little air is led to the combustion engine 1 that a combustion in the cylinders of the internal combustion engine is made impossible.

The combustion engine 1 here provides an emergency stop and damage due to overheating can be avoided.

Fig. 4 'shows an arrangement corresponding to the above-described arrangement which is additionally supplemented by a pressure sensor 15 which is arranged in the return line 9 downstream of the EGR cooler 1 1. The pressure sensor 15 senses the exhaust gas pressure after leaving the EGR cooler 1 1. 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 be aware of the pressure of the exhaust gases in the exhaust line 3 or the like so that the pressure drop of the exhaust gases 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 compare estimated values of the exhaust gas pressure drop as 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 11. The control unit 10 can set the second damper s here; in the cleaning mode at a subsequent operating mode when the first damper S1 is closed. This results in a real air flow at a high speed through the return line 9 and the EGR cooler 11, which effectively cleans the interior surfaces of the EGR cooler 1 1 from soot coatings.

Fig. 5 shows a fl fate diagram describing the function of the arrangements as above.

The process starts at 16. At 17, the control unit 10 receives information 14 regarding the internal combustion engine speed n. The control unit 10 compares whether the speed n is less than or equal to a maximum acceptable speed nmax. If the speed n is greater than the niaxially acceptable speed nmax, the Control Unit, at 18, opens the first damper s1 if it is not already open and puts the second damper sz in the cleaning position. In this case, an emergency stop is provided by the internal combustion engine 1 so that an overspeeding of the internal combustion engine 1 is prevented. Then the process restarts at 16.

If the control unit 10 finds that the speed n is acceptable, the process continues. at 19. where the control unit 10 receives information 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, at 20, places the first damper s1 in a open position and the second damper s; in a normal mode. If the Control Unit 10 simultaneously receives information from, for example, the pressure sensor 15 which indicates that the EGR cooler 11 needs to be cleaned, this may have to wait until a later, more opportune time when a clogging process of an EGR cooler 11 is usually not so urgent that it must be rectified immediately. . Then the process starts again at 16.

If the Control Unit 10 instead receives information 14 which indicates a rapidly increasing load or reduced load of the tube combustion engine 1, it states that the recirculation of exhaust gases through the return line 9 must be stopped. The control unit 10 then, at 21, places the first damper S1 in a closed position. Then the control unit decides. at 22. if the EGR cooler 1 1 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 23, keeps the second valve member sg in a normal 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 damper s is set; in a cleaning position at 24. Thus, a large air flow is obtained at a high speed through the EGR cooler 11 so that its inner surfaces are cleaned of soot coatings. With such regular cleanings of the EGR cooler, it can maintain good performance for a long period of operation without the need for service work to clean or replace it.

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 into 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 figures is illustrated by means of 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 the 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 memory), 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. Alternatively, the data carrier may 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 embodiments described in the drawing but can be varied freely within the scope of the claims. The invention is applicable to essentially all types of internal combustion engines where air is supplied with an overpressure to the internal combustion engine.

Claims (16)

10 15 20 25 30 35 528 881 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 internal combustion engine (1), a return conduit (9) arranged to recirculate exhaust gases from an exhaust line (3) of the internal combustion engine (1) to a connection point (12) with the inlet line (6) and an EGR cooler (11) arranged in the return line (9) for cooling the exhaust gases, characterized in that the arrangement comprises a valve means (S2) arranged in the inlet line (6), a line (13). extending from the valve means (s2) to a connection point (9a) with the return line. which connection point (9a) is located upstream of the EGR cooler (11) with respect to the intended flow direction of the exhaust gases in the return line (9), and a control unit (10) which, at certain times, is arranged to set the valve means (S2) in a cleaning position so that at least a part of the compressed air in the inlet line (6) is led via the valve member (s2) and said line (13), to the return line (9) where the air is led in a direction so that it flows through the EGR cooler (11 ). Arrangement according to claim 1, characterized in that the return line (9) comprises an EGR valve (si) which is arranged to control the flow of exhaust gases from the exhaust line (3) to the return line (9) and that said line (13a) of the dry line (9a). ) with the return line is located downstream of the EGR valve (sl) but upstream of the EGR cooler (1 1) with respect to the intended flow direction of the exhaust gases in the return line (9). Arrangement according to claim 2, characterized in that the control unit (10) is arranged to set the valve means (S2) in the cleaning position during operating condition of the internal combustion engine (1) when the EGR valve (si) is closed. Arrangement according to any one 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 (II) and to inform the control unit (10) of said parameters. value. Arrangement according to claim 4, characterized in that the control unit (10) is arranged to set the valve means (S2) in a cleaning position at times when it has received values regarding said parameter which indicate that the degree of occupancy in the EGR cooler (II) exceeds a maximum acceptable value. 'IO 15 20 25 30 35 528 881 11 Arrangement according to any one of the preceding claims 2 to 5, characterized in that the control unit (10) is arranged to receive information regarding the speed (n) of the internal combustion engine and that the control unit (10) is arranged to set the valve means (S2) in said cleaning position and the EGR valve (si) in an open position if the internal combustion engine speed (n) exceeds a maximum acceptable speed value (nmat). Arrangement according to one of the preceding claims, characterized in that the inlet line (6) comprises a compressor (5) which compresses the air in the inlet line and that the valve means (s2) is located downstream of the compressor (5) with respect to the flow direction of the air in the inlet line (6). . Arrangement according to claim 7, characterized in that the inlet line (6) comprises a charge air cooler (7) and that the valve means (S2) is located upstream of the charge air cooler (7) with respect to the air flow direction in the inlet line (6). A method of recirculating exhaust gases of an overcharged internal 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 connection point (12) with the inlet line and to cool the exhaust gases in the return line (9) in an EGR cooler (II) is shown by the steps of arranging a valve means (s2) in the inlet line (6) to arrange a line (13) extending from the valve means (s2) to a connection point (9a) with the return line, which connection point (9a) is located upstream of the EGR cooler (1 1) with respect to the intended flow direction of the exhaust gases in the return line (9), and at certain times placing the valve means (s2) in a cleaning position in which at least a part of the compressed air in the inlet line (6) is led via the valve means (s2) and said line (13), to the the discharge (9) where the air is led in one direction so that it flows through the EGR cooler (l 1). 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 an EGR valve (s |) and arranging the connection point (9a) of said line (13) with the return line downstream of the EGR the valve (S1) but upstream of the EGR cooler (1 1) with respect to the intended flow direction of the exhaust gases in the return line (9). '10 15 20 528 881 12 Method according to claim 10, characterized in that the valve means (sz) is in the cleaning position during the operating condition of the internal combustion engine (1) when the EGR valve (st) is closed. Method according to one of the preceding claims 9 to 1, characterized by the step of sensing a parameter which is related to the degree of occupancy of impurities in the EGR cooler (1 1) by means of a sensor (15). Method according to claim 12, characterized by the step of setting the valve means (s2) in a cleaning position at times when the value of said parameter indicates that the degree of coatings in the EGR cooler (11) exceeds a maximum acceptable value. A method according to any one of the preceding claims 10 to 13, characterized by the steps of receiving information regarding the speed (n) of the combustion engine and placing the valve means (S2) in said purification position and the EGR valve (si) in an open position for combustion. the engine speed (n) exceeds a maximum speed value (nmax). 15. A computer program, directly loadable to the internal memory of a computer. comprising software for controlling the method, according to any one of claims 9 -14 when the program is run on a computer. A computer readable medium (l0a) on which a program is stored, which is adapted to cause a computer to control the method according to any one of claims 9 -14.