FI124805B - COMBUSTION ENGINE AND A METHOD OF CONTROLLING ITS OPERATION - Google Patents

Description

AN INTERNAL COMBUSTION ENGINE AND A METHOD OF CONTROLLING THE

OPERATION THEREOF

Technical field The present invention relates to an internal combustion engine and a method of controlling the operation of an internal combustion engine. More specifically, the present invention discusses a two-stage Turbocharged Internal Combustion Engine having an SCR Catalyst for reducing the engine emissions and controlling the temperature of the exhaust gas Entering the SCR Catalyst.

Background art The requirements for exhaust gas emissions from internal combustion engines become more and more stringent. In order to fulfill such requirements there are various techniques available by means of which the gaseous emissions may be controlled when the engine is running. Naturally, it is clear that the overall performance of the engine should not suffer from actions aimed at reducing emissions. As examples of the most promising means may be mentioned two-stage turbocharging and use of an SCR Catalyst (SCR stands for Selective Catalytic Reduction).

[003] By two-stage turbocharging is understood as an arrangement where two turbochargers have been arranged in a series of exhaust and inlet pipings of an internal combustion engine. The turbochargers are called a low-pressure (LP) turbocharger with a low-pressure compressor and a low-pressure turbine, and a high-pressure (HP) turbocharger having a high-pressure compressor and a high-pressure turbine. The exhaust gas discharged from the engine cylinders is first taken to the high-pressure turbine which rotates the high-pressure compressor and the next to the exhaust gas is taken to the low-pressure turbine which rotates the low-pressure compressor. Fresh air is first taken to the low-pressure compressor, and then to the high-pressure compressor, wherever the charge air is taken to the engine cylinders. The operation of the two turbochargers is controlled by means of by-pass pipes arranged on either side (compressor or turbine) or both sides of the turbochargers. The basic idea is to control the operation of the turbochargers in all possible loads of the engine such that the best engine efficiency and the lowest emissions are achieved. Thus, the turbochargers may be arranged to run without any by-pass whereby both the exhaust gas and the fresh air flow through both turbochargers. Another option is to arrange a partial by-pass such that only a portion of the exhaust gas and / or fresh air flows through both turbochargers. And yet a further option is that one of the turbochargers is by-passed entirely whereby the exhaust gas and / or the fresh air flows through only one turbocharger. In the following few documents discussing two-stage turbocharging have been referred to.

WO-A1-2004097195 discusses a turbocharger device for an internal combustion engine, comprising at least one exhaust turbocharger, which may be driven by an exhaust gas from an internal combustion engine and a compressor of which are arranged in an air Inlet line and are provided for compression of combustion air for internal combustion engine. A serial arrangement of a turbine and a first exhaust gas Catalyst are provided in the exhaust line. The switchable bypass line is also provided through which an exhaust gas mass flow may run, which branches off the exhaust line upstream of the serial arrangement and returns again at a Junction downstream of the serial arrangement in the exhaust line.

WO-A1-2008069780 discusses an engine arrangement including an engine, an exhaust line downstream of the engine, an after treatment device in the exhaust line, and a conduit between a source of fluid and a point in the exhaust line upstream of the after treatment device.

DE-A1-102 22 919 discusses an internal combustion engine provided with a two-stage turbocharging arrangement and a special valve arrangement controlling the flow of the exhaust gas. The valve arrangement may be used for the recirculation of the exhaust gas to the intake of the engine, for the guiding exhaust gas to the high pressure turbine, and for the guiding exhaust gas to the low pressure turbine, ie, bypassing the high -pressure turbine. Additionally, the valve arrangement may be used as an exhaust brake, too.

EP-A2-1275832 discusses an internal combustion engine with two-stage turbocharging. The document teaches how to arrange by-pass pipes with adjustable valves to the side of the high-pressure turbo, both the compressor and the turbine of the high-pressure turbo may be either partially or totally by-passed, whereby the engine may be adapted to varying load conditions.

WO-A1-2010112718 discusses an internal combustion engine provided with a two-stage turbocharging arrangement with means for bypassing a high-pressure turbine, a low-pressure turbine and a high-pressure compressor. Specifically, the document is concerned with controlling the by-pass pipe of a turbocharger in a view of emission standards and engine performance.

Selective Catalytic Reduction (SCR) is a means of converting nitrogen oxides, also referred to as NOx, to a catalyst of diatomaceous nitrogen, N2, and water, H2O. The reductant, typically urea, is added to the stream of exhaust gas and is absorbed onto the Catalyst. Carbon dioxide, CO2, is a reaction product when urea is used as a reductant. SCR has proven to be an advantageous method for maintaining gaseous emissions from internal combustion engines at a low level. SCR has been utilized with success in connection with both 2- stroke and 4- stroke Turbocharged internal combustion engines. The positioning of the SCR Catalyst in the exhaust Piping has been variably either between the engine and the turbocharger, or after the turbocharger. Lately, SCR Catalyst has also been proposed to be used in combination with two-stage turbocharging. In the following few documents discussing internal combustion engines with both two-stage turbocharging and SCR Catalyst have been referred to.

WO-A1-2010052055 discusses one embodiment of an internal combustion engine having a two-stage turbocharging arrangement with two oxidation catalysts, a denitrification arrangement and a particulate filter. The first oxidation catalyst is located between the engine and the high pressure turbine, the denitrification arrangement either before or after the high pressure turbine in the exhaust piping, and the second oxidation catalyst and the particulate filter after the low pressure turbine. The exhaust piping is additionally provided with an exhaust by-pass pipe bypassing the first oxidation catalyst, the denitrification arrangement and the high-pressure turbine. The by-pass pipe is provided with an adjustable valve that opens at high load so that the denitrification arrangement is not subject to excessive thermal loads, but the particulate filter after the low-pressure turbine may still be regenerated by means of the hot exhaust gas. In another embodiment, the denitrification arrangement is arranged after the high-pressure turbine and the by-pass pipe, whereby the NO2 / NO- ratio of the denitrification arrangement may be controlled by the valve in the by-pass pipe.

WO-A1-2004097195 discusses an internal combustion engine provided with a two-stage turbocharging arrangement with a Catalyst arranged between the turbines. There are two by-pass pipes arranged in the exhaust pipe system. One bypassing the high-pressure turbine and the Catalyst, and the other bypassing the low-pressure turbine. Both by-pass pipes are provided with valves. Additionally, an exhaust gas recirculation from the exhaust manifold to the charge air duct between the compressors is arranged.

Thus, when aiming at still lower engine emissions, the two-stage turbocharging and the selective catalytic reduction have been taken into simultaneous use in the internal combustion engines. The SCR Catalyst has naturally three possible different positions in the exhaust pipe. In other words, it can be located in the exhaust pipe between the engine and the HP turbine, between the HP turbine and the LP turbine, or after the LP turbine. An important factor regarding the positioning of the SCR Catalyst is the temperature of the exhaust gas Entering the Catalyst. As the optimum operating temperature of the SCR Catalyst is from about 350 ° C to about 420 ° C, it is a natural to position the SCR Catalyst to a location where the exhaust gas temperature is high, preferably most of the operating time of the engine within that temperature range or very close to that. However, as soon as the value of the engine load is changed from its optimum (in view of the SCR operating temperature) value, the temperature of the exhaust gas is either raised or lowered. Thereby, the temperature of the SCR Catalyst goes easily beyond the optimum temperature range, and the efficiency of the Catalyst is reduced. For the reason above, the SCR Catalyst has normally been positioned between the HP and the LP turbines, where the temperature control is, for natural reasons, the easiest.

The above-mentioned WO documents discuss an internal combustion engine having an SCR Catalyst arranged between the HP and LP turbines of the two-stage turbocharger arrangement. WO-A1 -2010052055 teaches the presence of a control valve in a by-pass pipe by-passing the HP-turbine and introducing the exhaust gases upstream of the SCR Catalyst, but the valve and its control are there for controlling the NO2 / NO - ratio not controlling operation of SCR Catalyst.

Thus, an object of the present invention is to find a proper location for the SCR Catalyst in the exhaust piping when the SCR Catalyst is arranged in connection with a two-stage turbocharged internal combustion engine.

[0015] It is another object of the present invention to provide a control arrangement for a two-stage turbocharged internal combustion engine with an SCR Catalyst for maintaining gaseous emissions at a low level in all operating conditions of the engine.

It is also an object of the present invention to provide a method of controlling the temperature of an SCR Catalyst used in connection with a two-stage turbocharged internal combustion engine so that the SCR Catalyst is capable of operating at its optimum temperature.

It is also a further object of the present invention to introduce a number of methods for controlling the temperature of an SCR Catalyst used in connection with a two-stage turbocharged internal combustion engine.

Disclosure of the Invention At least one of the above and other objects of the invention are met by an internal combustion engine, the engine having an exhaust manifold attached to an exhaust pipe, a charge air receiver attached to a charge air pipe, a high-pressure turbocharger having a high-pressure turbine and a high-pressure compressor, a low-pressure turbocharger having a low-pressure turbine and a low-pressure compressor, an SCR Catalyst arranged between the high-pressure turbine and the low- pressure turbine, high pressure turbine arranged in flow communication with exhaust manifold by means of first exhaust pipe section and with low pressure turbine by means of second exhaust pipe section, by low pressure turbine being further in flow communication with a third exhaust pipe section, a charge air pipe including a first charge air pipe section between a charge air receiver and a high pressure compressor and a second charge air pipe section between the high-pressure compressor and low-pressure compressor, the engine further comprises means for affecting the temperature of the exhaust gas in the second exhaust pipe section, and means (ECU) for controlling the temperature affecting means, charge air waste gate arranged for first charge air pipe section, second charge air pipe section and / or charge air distributor for raising the temperature of the exhaust gas Entering the SCR Catalyst in the second exhaust pipe section, and a temperature indicator te arranged upstream of SCR Catalyst (20) in second exhaust pipe section (12) for inputting temperature value into ECU.

[0019] At least one of the above and other objects of the invention is a method of controlling the operation of an internal combustion engine, the engine having an exhaust manifold attached to an exhaust piping, a charge air receiver attached to a charge air piping, high pressure turbocharger having high pressure turbine and high pressure compressor, low pressure turbocharger having low pressure turbine and low pressure compressor, an SCR Catalyst arranged between the high pressure turbine and the low pressure turbine, the high pressure turbine arranged in flow communication with the exhaust manifold by means of the first exhaust pipe section and the low pressure turbine with the second exhaust pipe section, the low pressure turbine being further in flow communication with a third exhaust pipe section, a charge air pipe section including a first charge air pipe section between a charge air receiver and a high pressure compressor and a second charge air pipe section between the high-pressure compressor and the low-pressure compressor, the engine further comprising means for affecting the temperature of the exhaust gas in the second exhaust pipe section, the method comprising the steps of providing the first charge air pipe section, the second charge air pipe section and / or charge air distributor with charge air waste gate valve for heating exhaust gas temperature in second exhaust pipe section upstream of SCR Catalyst, monitoring positions of charge air waste gate valve, and inputting monitored position value in the control unit (ECU), monitoring the temperature t6 in the second exhaust pipe section upstream of the SCR Catalyst, inputting the monitored temperature value in the control unit (ECU), and controlling the charge air waste gate valve for adjusting the temperature of exhaust gas upstream of SCR Catalyst for maintaining temperature of second exhaust pipe section upstream of SCR Catalyst w ithin a desired range.

Other characteristic features of the present invention will become apparent from the appended dependent claims.

The present invention, when solving at least one of the above-mentioned problems, improves the emission control of internal combustion engines.

Brief Description of the Drawing The present invention is explained in more detail with reference to the accompanying figures, of which

Figure 1 illustrates schematically a prior art internal combustion engine provided with two-stage turbocharging,

Figure 2 illustrates schematically the internal combustion engine in accordance with the first preferred embodiment of the present invention,

Figure 3 illustrates schematically the internal combustion engine in accordance with the second preferred embodiment of the present invention,

Figure 4 illustrates schematically the internal combustion engine in accordance with the third preferred embodiment of the present invention,

Figure 5 illustrates schematically the internal combustion engine in accordance with the fourth preferred embodiment of the present invention,

Figure 6 illustrates schematically the internal combustion engine in accordance with the fifth preferred embodiment of the present invention,

Figure 7 illustrates schematically the internal combustion engine in accordance with a sixth preferred embodiment of the present invention, and

Figure 8 illustrates schematically a few alternatives for controlling the operation of the embodiments of the present invention discussed in connection with Figures 2-7.

Detailed Description of Drawings Figure 1 illustrates schematically a prior art internal combustion engine provided with two-stage turbocharging. The engine unit, i.e. the cylinders, the cylinder block and the cylinder head / s are shown by reference numeral 1. The internal combustion engine is also provided with two turbochargers, viz. a high-pressure (HP) turbocharger 2 having an HP-turbine 3 and an HP-compressor 4 and a low-pressure (LP) turbocharger 5 having an LP-turbine 6 and an LP-compressor 7. An exhaust manifold 8 is attached at its one end to the engine unit 1 in flow communication with its exhaust ports (not shown), and at its opposite end to an exhaust Piping formed of three exhaust pipe sections. The exhaust manifold 8 is arranged in flow communication with the HP turbocharger 3 by means of the first exhaust pipe section 9 for taking the exhaust gas from the engine cylinders to the HP turbocharger 2. The HP turbine 3 is arranged in flow communication with the LP-turbine 6 by means of a second exhaust pipe section 12. The LP-turbine 6 discharges the exhaust gas to a third exhaust pipe section 13, which may, if desired, be provided with a particulate filter. A charge air receiver 10 which could also be called as the Inlet manifold is also attached to the engine unit 1 for introducing a charge air into the Inlet ports (not shown) of the engine unit 1. The charge air receiver 10 connects the engine unit to charge air piping, and is arranged in flow communication with HP-compressor 4 by means of first charge air pipe section 11. combustion air enters engine and LP-compressor 7 via an intake air silencer 14. From the LP-compressor 7 a second charge air pipe section 15 takes the charged air to the HP- compressor 4.

Figure 1 also shows how the charge air path from the intake silencer 14 to the charge air receiver 10 is provided with the charge air intercooler 16 arranged in the second charge air pipe section 15 between the LP and the HP compressors, and with a charge air aftercooler 17 arranged in the first charge air pipe section 11 between the HP-compressor 4 and the charge air receiver 10. Naturally, it has to be understood already at this stage, the presence of both intercooler 16 and the aftercooler 17 or the presence of one of them is not necessary for the working of the invention. However, the use of charge air coolers 16 and 17 is advantageous as it increases greatly the efficiency of the internal combustion engine.

[0025] When an SCR Catalyst 20 is installed in the exhaust gas path or exhaust Piping of an internal combustion engine provided with a two-stage turbocharging of the best location for the SCR Catalyst 20 is in the second exhaust pipe section 12 between the HP- and LP-turbines as shown in Figure 2. The temperature range for the SCR Catalyst is, in general, too low after the LP-turbine 6 and too high before the HP-turbine 3. However, when the SCR Catalyst 20 is located between the turbines in a two-stage turbocharged engine, the temperature of the SCR Catalyst is easily in the upper end of the desired temperature range of the SCR Catalyst 20, although sometimes the temperature of the SCR Catalyst may tend to decrease below the desired lower limit value . As mentioned earlier, the proper operating temperature of an SCR Catalyst is from about 350 ° C to about 420 ° C. Thus, the temperature of the exhaust gas Entering the Catalyst has to be monitored and adjusted whenever needed. Figures 2 through 4 illustrate a few preferred embodiments for lowering the temperature of the exhaust gas Entering the SCR Catalyst, and Figures 5 through 7 illustrating a few preferred embodiments for raising the temperature of the exhaust gas Entering the SCR Catalyst.

[0026] In accordance with Figure 2, a first preferred embodiment of the present invention discusses a couple of ways of lowering the temperature of the exhaust gas Entering the SCR Catalyst 20. The cooling of the exhaust gases comes into question only in exceptionally high loads of the engine, but also ambient air has an effect on the exhaust gas temperature. In other words, the hotter are the suction air temperature and the coolant (charge air cooler) temperature, the higher is the exhaust temperature. The cooling of the exhaust gases is accomplished, the present invention, by the introduction of the air, the preferred charge air, the exhaust gas upstream of the SCR Catalyst 20 into the second exhaust pipe section 12. In order to be able to introduce the air among the exhaust gas the air to be introduced has to be at a higher pressure. At high loads the charge air is in overpressure compared to exhaust gases. At engine loads of roughly 30% - 100% pressure is higher at charge air receiver 10. At engine loads below -30% pressure is higher at exhaust Piping, whereby air bypass cannot be used. However, such is not needed as the temperature of the exhaust gases Entering the SCR may, at such a low engine load, be even too low. Thus, the first option to find air at a sufficient pressure is to arrange an air by-pass (ABP) pipe 22 to introduce air from the charge air receiver 10 or slightly upstream sign, i.e. after the HP-compressor 4 from the first charge air pipe section 11, to the second exhaust pipe section 12 upstream of the SCR Catalyst 20. The air flow is controlled by an adjustable valve 24 and the air is introduced to the pipe section 12 by means of a Distributor 26 which mixes the air evenly to the exhaust gas such that the temperature of the exhaust gas is lowered evenly before the combination of gases enter the SCR Catalyst 20.

[0027] A second option to find air at a sufficient pressure, though at a lower pressure than the first option discussed, is to arrange an air by-pass pipe 28 with an adjustable valve 30 from a second charge air pipe section 15. after the intercooler 16 (if such exists), ie downstream signage to take charge air to second exhaust pipe section 12 upstream of SCR Catalyst 20. And naturally, third option is to have both pipes 22 and 28 collect cooling air and control cooling air introduction by means of adjustable valves 24 and 30 arranged in both by-pass pipes 22 and 28. The by-pass pipes 22 and 28 may have a common inlet conduit to the Distributor 26 as shown in Figure 2, but the by-pass pipes 22 and 28 may also extend as separate pipes all the way from their origin in charge air Piping to the Distributor 26. Even a separate Distributor for each charge air by-pass pipe may be considered. The air for cooling the exhaust gas may also be taken before one or both of the charge air coolers 16 and 17, if such exist / s, but, as long as cooling is the main purpose of the air introduction to the exhaust gas upstream of the SCR Catalyst 20, it is naturally preferable to take the air after one or both of the coolers, the cooler the charge air is the less charge air is needed to cool the exhaust gas upstream of the SCR Catalyst, and the less the charge air by-pass interferes in the operation of the HP-compressor 4.

Figure 2 also shows an electronic control unit (ECU) that is used for controlling the valves 24 and 30, for instance by means of the pressure (ρβ) and temperature (ΐβ) data collected from the second exhaust pipe section 12 upstream of the SCR Catalyst 20.

Figure 3 illustrates schematically as a second preferred embodiment of the present invention the cooling air introduction directly to the exhaust manifold 8 or to the first exhaust pipe section 9. The cooling air is again taken from the charge air receiver 10 or slightly upstream sign from the first charge air pipe section 11 to an air bypass pipe 32 and introduced, in the first option, to the first exhaust pipe section 9 upstream of the HP turbine 3. The introduction of the air is controlled by an adjustable valve 34 arranged in the charge air by-pass pipe 32. A second option is to connect the air by-pass pipe 36 to the exhaust manifold 8. In view of these two options it is clear that the air admission in the exhaust Piping may be done in any position upstream of the HP-turbine 3. In this embodiment no Distributor of cooling air is needed when introducing the air among the exhaust gas, as the HP-turbine 3 mixes the air evenly with the exhaust gas. Figure 3 illustrates an electronic control unit (ECU) that is used for controlling the valves 34, for instance, by means of the pressure (pe) and temperature (te) data collected from the second exhaust pipe section 12 upstream of the SCR Catalyst 20.

Figure 4 illustrates a third embodiment of the present invention for injecting water to the exhaust gas upstream of the SCR Catalyst 20. One option is to arrange the water injection 40 to the exhaust manifold 8 or to the first exhaust pipe section 9 thereafter, in any case, upstream of the HP-turbine 3, and another option is to arrange the water injection 42 to the second exhaust pipe section 12 directly upstream of the SCR Catalyst 20. Water is efficiently cooled down to the excess exhaust gas temperature. Naturally, also water injection is controlled by means of valves 44 and 46 or some other appropriate means. Figure 4 illustrates an electronic control unit (ECU) that is used for controlling valves 44 and 46, for instance by means of pressure (ρβ) and temperature (ΐβ) data collected from the second exhaust pipe section 12 upstream of the SCR Catalyst 20.

Sometimes the temperature of the exhaust gas Entering the SCR Catalyst 20 is not sufficient. Such can happen, for instance, when performing a cold start of the engine, at low loads and / or when Variable Inlet Valve Closure (VIC) is in full use. 2-stage Turbocharged engines operate with early miller timing and part load variable Inlet valve closing (VIC) is utilized. VIC means that the inlet valve can be closed later, meaning reduced Miller effect and, as a result, increased amount of air into cylinder / s. The increased amount of air again lowers the exhaust gas temperature. Figures 5-7 discuss a few alternatives for heating the exhaust gas before introducing such to the SCR Catalyst.

[0031] Figure 5 discusses a fourth preferred embodiment of the present invention, a novel alternative to reducing the boost and thus increasing the exhaust gas temperature in the second exhaust pipe section 12 upstream of the SCR Catalyst 20. In this embodiment, a waste gate or exhaust by-pass pipe 60 is arranged to by-pass the LP-turbine 6, whereby the exhaust or part is taken to the outlet by the LP-turbine 6 or to the third exhaust pipe section 13. The control of the by -pass flow is performed by means of an adjustable valve 62 in the by-pass pipe 60. The by-pass pipe 60 may branch from the second exhaust pipe section 12 either as shown in Figure 6, ie between the SCR Catalyst 20 and the LP- turbine 6, or upstream of the SCR Catalyst 20. Figure 5 illustrates, again, the electronic control unit (ECU) that is used for controlling the valve 62, for instance by means of pressure (p6) and temperature (t6) data collected from the second exhaust pipe section 12 upstream of the SCR Catalyst 20.

Figure 6 discusses the fifth embodiment of the present invention exhaust bypassing of both turbines 3 and 6. In other words, the waste gate or exhaust by-pass pipe 70 is arranged to run from the exhaust manifold 8 or the first exhaust pipe section 9 upstream of the HP- turbine 3 to the outlet of the LP- turbine 6 or to the third exhaust pipe section 13. Thus, a part of the hot exhaust gas, controlled by an adjustable valve 72, is taken in practice directly from the exhaust manifold 8 to the exhaust gas discharge. The heating of the SCR Catalyst 20 is thus based on the lower overall boost level. Figure 6 illustrates once again the electronic control unit (ECU) that is used for controlling the valve 72, for instance by means of the pressure (ρβ) and temperature (te) data collected from the second exhaust pipe section 12 upstream of the SCR Catalyst 20.

The arrangement of Figure 6, i.e. the by-passing of both turbines has proven to be especially advantageous for the following reasons. When using exhaust waste gate for controlling the temperature of the SCR between the HP- and LP-turbines, there are three options to practice, either to arrange the exhaust waste gate over or to arrange the exhaust waste gate over both turbines.

Performed experiments have shown that when the exhaust waste gate is arranged over the HP turbine and the ambient temperature decreases, the operating point of the LP compressor, in the compressor map, moves up towards the surge line. If the engine load is increased, while the exhaust waste gate is arranged over the HP turbine, the operating point moves straight up towards, and finally over, the surge line. Such cannot be accepted as the engine has to be able to tolerate overload.

[0035] In a similar manner, the experiments have shown that when the exhaust waste gate is arranged over the LP-turbine and the ambient temperature is reduced, the operating point of the LP-compressor moves down substantially parallel with the surge line, i.e. the compressor speed decreases. If the engine load is increased, while the exhaust waste gate is arranged over the LP-turbine, the operating point moves straight down. In both cases, the speed of the HP-compressor increases and its operating point moves up. For compensating for the operation of the LP- compressor the HP- turbine should have a speed margin in both cold and overload conditions, but, as the speed of the HP- turbine has already increased, there is no speed margin available.

The experiments have, however, shown that when arranging the exhaust waste gate over both turbines, the operating point remains in place irrespective of the load. Thus, for overload conditions, the EWG over both turbines is the optimum choice.

In cold operating conditions, when using EWG over both turbines, the operating point of the LP-compressor, however, moves along the surge line while the compressor speed remains substantially the same. This feature is not acceptable and brings in the need for compensating the transfer tendency of the operating point. The performed experiments have shown that opening the air bypass (ABP) (shown by reference numbers 22 and 32 in Figures 2, 3 and 8) is a suitable remedy for maintaining the position of the operating point substantially optimal on the compressor map. Simultaneously, the ABP affects in lowering the SCR temperature.

Figure 7 discloses a sixth embodiment of the present invention where the charge air may be discharged either via an adjustable (or on / off) valve 80 (so called Air Waste Gate, AWG) from the second Inlet section 15 after the intercooler 16 or via an adjustable (or on / off) valve 82 from the charge air receiver 10 or from the charge air receiver and the charge air cooler 17. Naturally, the Air Waste Gates (AWG) 80 and 82 could be arranged just downstream of the LP- and / or HP- compressors 7 and / or 4, too, ie upstream of charge air coolers 16 and 17. However, if the AWG is arranged upstream of the charge air coolers, the temperature of the charge air may be so high that the air from the AWG cannot be discharged to the engine room but is, for instance, discharged to the exhaust pipe after the LP-turbine 6. By reducing the amount of charge air (by opening the AWG valve / s), and the boost, the temperature of the exhaust gases is raised. Figure 7 also shows an electronic control unit (ECU) that is used for controlling the valves 80 and 82, for instance by means of pressure (ρβ) and temperature (t6) data collected from the second exhaust pipe section 12 upstream of the SCR Catalyst 20.

Yet another way (not shown) of influencing the temperature of the exhaust gas is to enter the SCR Catalyst 20 to control the Variable Inlet Valve Closing (VIC). In practice VIC is used at part load and it can also be used to control SCR temperature. If the temperature is too low (at part load) the valve closing may be advanced, whereby the SCR temperature increases. At part load it may be the only way to increase SCR temperature.

At this stage it has to be understood that all of the above discussed ways of affecting the exhaust gas temperature upstream of the SCR Catalyst may be used in connection with a single internal combustion engine. Thus, the division of the ways of affecting the exhaust gas temperature in separate embodiments is done for the sake of clarity only. In other words, it is clear that the two or more discussed ways of affecting the exhaust gas temperature upstream of the SCR Catalyst may be used together depending on the emission requirements of the engine or desires of the user.

Thus, for instance, the preferred alternative is to use the connection with the exhaust by-pass 70 of Figure 6, the air by-pass 32 or 36 of Figure 3, and the air waste gate 80 or 82 of Figure 7. The main functions are as discussed above, as follows: exhaust by-pass for heating the SCR Catalyst, air by-pass for cooling the exhaust, and air waste gate for protecting the engine against too high firing pressures and surging due to cold suction air. When the engine is provided with a set of controls like the ones discussed above, the operator is able to run the engine in all imaginable conditions, including starting and running the engine at low and high temperatures and changing the engine load rapidly.

Without saying it is clear that the various adjustable valves discussed in connection with the above embodiments need a control system. Figures 2 through 7 have shown an electronic control unit (ECU) and discussed such a brief, but now the control system will be discussed in more detail. Figure 8 discusses a few different alternatives for the control system. One way of controlling the operation of the valves is to measure or monitor the temperature directly at the entrance of the SCR Catalyst 20 in the second exhaust pipe section 12. Thus, depending on the temperature indication, the ECU instructs the control valves of the charge air by-pass pipes, and / or water injection and / or exhaust waste Gates and / or charge air waste Gates to open or close.

For instance, if you specify a temperature below the desired SCR Catalyst temperature window, the ECU instructs at least one of the exhaust gas waste gate or by-pass pipe valves 62 and 72, or charge air waste gate valves 80 and 82 (shown in Figures 5 - 7) to open. Or, if only the charge air by pass is available for controlling the temperature of the exhaust gas, i.e. to cool down the exhaust gas Entering the SCR Catalyst 20, the ECU instructs one or more of the valves 24, 28 and 34 (shown in Figures 2 and 3) to be throttled, i.e. to reduce cooling air flow, or to close such completely.

In a similar manner, if water injection is used to control the temperature, the ECU instructs feed water to be reduced by means of valve / s 44 and / or 46 (shown in Figure 4) for increasing the temperature of the exhaust gas. Also if charge air by-pass and / or exhaust by-pass and / or water injection are utilized in combination, it is possible to reduce the cooling effect by throttling, or closing, one or more charge air by-pass valves 24, 28, and 34 (shown in Figures 2 and 3) or one or more water injection valves 44 and 46 (shown in Figure 4), and / or increasing the heating effect by opening one or more exhaust by-pass valves 62 and 72 (shown in Figures 5 and 6), or charge air waste gate valves 80 and 82 (shown in Figure 7). Naturally, if the goal is to cool down the SCR Catalyst temperature, the actions to be performed are opposite.

The following table shows, referring to Figures 2-7, the options there are available for controlling the temperature of the SCR Catalyst. The table should read such that for both heating and cooling there are eight variables, valves or like, with which the SCR Catalyst temperature may be changed. The leftmost column shows the variable, i.e. the valve in question, which naturally refers to the use of the entire bypass pipe or water injection. The two columns show the desired action regarding the SCR Catalyst temperature. The sign indicates that the valve should be either closed or at least throttled for decreasing flow in the pipe in question. The '+' signifies that the valve should be completely open or at least opened for increasing the flow in the pipe in question.

As mentioned above, the number of SCR temperature control means can change depending on, for instance, the application in question, the accuracy of the desired control, the desires of the user, etc. Thus, the above table should be understood that if the heating is the only action needed, ie, if the exhaust gas temperature is either appropriate for the SCR Catalyst operation or too low, the internal combustion engine needs to be provided with only means for heating the exhaust gas upstream of the SCR Catalyst. Such means have been shown in the 'Heating' column by '+' sign, i.e., the engine has been provided with one or more such means. In a corresponding manner, if the gas only needs to be cooled upstream of the SCR Catalyst, the engine has to be provided with one or more means shown by the '+' sign in the 'Cooling' column. And, in the most probable option, when the gas is entering the SCR Catalyst need to be either cooled or heated depending on the instance, the load is on the engine, the engine has to be provided with at least one means having a '+' sign in the 'Cooling' column, and with at least one means having a '+' sign in the 'Heating' column.

Another applicable control mechanism is also shown schematically in Figure 8 is based on monitoring the boost pressure p3 in the charge air receiver 10, the charge air pressure pi in the intercooler 16 in the second inlet section 15 and the exhaust gas pressure ρβ after the HP-turbine 3 in the second exhaust pipe section 12. In addition to those temperature and / or pressure measurements the engine load and the VIC position are monitored, too. When these parameters are inputted in the control unit (ECU), the control unit may, by using maps pre-programmed in the memory of the control unit, control the positions (ie opening angles) of one or more of the air by-pass valves 24, 28 and 34, exhaust gas waste gate or by-pass valves 62 and 72, feed water injection valves 44 and 46, and air waste gate valves 80 and 82 to ensure proper temperature for the SCR Catalyst 20. The benefit of these pre-programmed or predefined maps are the quick response they give. Compared to measuring directly the exhaust gas temperature, you get results in a slow response as the reaction to load changes, etc. is very slow.

The above-mentioned maps may be created by running actual tests covering all possible variations of the following: boost pressure p3 in charge air receiver 10, boost pressure in first charge air pipe section 11, charge air pressure pi after the charge air intercooler 16 in the second charge air pipe section 15, the exhaust gas pressure p6 after the HP-turbine 3 in the second exhaust pipe section 12, the engine load, the VIC position, the opening positions of each one of the air bypass valves 24, 28 and 34, the opening positions of each of the exhaust gas gates or by-pass valves 62 and 72, the opening positions (ie, opening angles) of each of the air waste gates 80 and 82 , and the opening positions (ie opening angles) of each one of the feed water injection valves 44 and 46 and the temperature of the second exhaust pipe section 12 upstream of the SCR Catalyst 20. Naturally, also other variables may be included in the maps like en gine emissions, efficiency, fuel consumption etc. This procedure results in a huge number of maps of only those having the temperature within the desired range are selected to be stored in the memory of the control unit.

The maps are used for controlling the SCR Catalyst temperature as follows. When running the engine at a certain load only such maps may be used that have the same load. Now that the temperature of the SCR Catalyst, or actually the gas Entering the Catalyst, approaches the boundary value of the desired temperature range or above such, the control unit chooses from the maps one giving the best overall performance. This may mean, for instance, minimum number of changes in the variables, smallest emissions, best efficiency etc. After the map is selected the control unit makes the required changes in the variables, for instance changes in the opening angle of one or more control valves. As an example, if a certain amount of water is injected upstream of the SCR Catalyst, and now the temperature approaches the lower limit of the temperature range, the control unit decreases the opening angle of the water injection control valve, whereby less water is injected, and the temperature is made to remain within the desired range.

[0050] Like the above example, the maps do not necessarily require a combination of all variables. In other words, also such combinations of variables are possible that change in a variable has an effect on only one or more variables in the combination, but not on a single variable outside the combination.

Another way of creating maps is a computerized model of operation of an internal combustion engine. Naturally, the functionality of a model may be checked by running experiments in different operating conditions of an engine.

[0052] As for the exact positions where the temperature and the pressures are measured, the temperature can be measured upstream of the Distributor 26, especially if it is a question of using a control unit utilizing a predefined map, whereby the temperature te gives the control unit has sufficient information for controlling the positions (ie opening angles) of one or more of the air by-pass valves 24, 30 and 34, the exhaust gas waste gate or by-pass valves 62 and 72, the air waste gate valves 80 and 82, and feed water injection valves 44 and 46. However, if it is a question of direct control of one or more of the air by-pass valves 24, 30 and 34, the exhaust gas waste gate or by-pass valves 52, 62 and 72, air waste gate valves 80 and 82, and feed water injection valves 44 and 46 by the position of the temperature measurement after the Distributor 26.

It should be understood that the above is only an exemplary description of the novel and inventive internal combustion engine, and a method of controlling the temperature of the SCR Catalyst therein. It should be understood that the above description discusses only a few preferred embodiments of the present invention without any purpose to limit the invention to the discussed embodiments and their details only. In other words, it is clear that the number of turbochargers is not limited to those two discussed in the exemplary embodiments, but it is possible that the engine may have one LP-turbocharger and two HP-turbochargers in parallel, or the engine may have one HP- turbocharger and two LP-turbochargers in parallel, or the engine may have two parallel LP- turbochargers and two parallel HP-turbochargers. In very large internal combustion engines, the number of turbochargers may even exceed the above examples. Thus, the above specification should not be understood as limiting the invention by any means but the entire scope of the invention is defined by the appended claims only. From the above description it should be understood that the separately discussed embodiments or features of the invention may be used in connection with the other separately discussed features, even if such a combination has not been specifically shown in the description or in the drawings.

Claims (22)

1. An internal combustion engine consisting of: • an exhaust manifold (8) attached to the exhaust pipe • a charge air reservoir (10) attached to the charge air pipe • a high pressure turbocharger (2) with a high pressure turbine (3) and a low pressure turbocharger (5) 6) and a low pressure compressor (7), an SCR catalyst (20) disposed between the high pressure turbine (3) and the low pressure turbine (6), - the high pressure turbine (3) being arranged in flow communication with the exhaust manifold (8) through the first exhaust pipe section (9) and with the low pressure turbine (6) via the second exhaust section (12), - the low pressure turbine (6) still in fluid communication with the third exhaust section (13), - the supercharging pipe comprising a first supercharging section (11) between the supercharging air tank (10) and a second compression air pipe section (15) between the high pressure compressor (4) and the low pressure compressor (7), for controlling the temperature of the gas in the second exhaust pipe section (12), and • devices (ECU) for controlling the devices affecting the temperature, characterized by • a compressed air waste port (80, 82) acting as a temperature affecting device arranged on the first compressor pipe section (11); ) and / or the charge air reservoir (10) for increasing the temperature of the exhaust gas entering the SCR catalytic converter (20) in the second exhaust section (12), and • a temperature sensor te provided in the second exhaust section (12) before the SCR catalyst (20). to enter a value in the ECU. An internal combustion engine according to claim 1, characterized in that the engine comprises cooling means (24, 30, 34, 44, 46) for lowering the temperature of the exhaust gas entering the SCR catalytic converter (20) in the second exhaust section (12). An internal combustion engine according to claim 1, characterized in that the engine further comprises heating means (62, 72) for increasing the temperature of the exhaust gas entering the SCR catalyst (20) in the second exhaust section (12). An internal combustion engine according to claim 1, 2 or 3, characterized in that the control device is a control unit arranged to selectively control at least one of the cooling devices (24, 30, 34, 44, 46) and / or at least one of the heating devices (62, 72, 80). 82) for controlling the temperature of the gas entering the SCR catalyst (20). 5. An internal combustion engine according to claim 1, characterized in that the engine further comprises a cooling device which is a charge air bypass pipe (22, 28, 32, 36) between the charge air pipe (11, 15) and the exhaust pipe (8, 9, 12). , 9, 12) to cool the exhaust stream prior to the SCR catalyst (20). An internal combustion engine according to claim 1, characterized in that the engine further comprises a heater which is an exhaust bypass tube (70) which bypasses the HP turbine (3), LP turbine (6) and SCR catalyst (20) to reduce the supercharging pressure in the charge air pipe for producing an exhaust stream upstream of the SCR catalyst (20). Internal combustion engine according to Claim 1, characterized in that the engine further comprises a cooling device, which is a water injection (40, 42) arranged in the exhaust pipe upstream of the SCR catalyst (20). An internal combustion engine according to claim 5 or 6, characterized by a distributor (26) located upstream of the SCR catalyst (20) for uniformly mixing the bypass air with the exhaust gas in the second exhaust section (12). An internal combustion engine according to claim 5, characterized by valves (24, 30, 34) disposed in the charge air bypass pipes (22, 28, 32, 36) for controlling the charge air bypass flow. An internal combustion engine according to claim 7, characterized by valves (44, 46) for controlling the amount of water injected into the exhaust pipe. An internal combustion engine according to claim 5 or 6, characterized by valves (72) disposed within the exhaust bypass (70) for controlling the exhaust bypass flow. An internal combustion engine according to any one of the preceding claims, characterized by an HP compressor provided with a pressure transducer pi provided in front of the second exhaust section (12) to supply a pressure value to the ECU. An internal combustion engine according to any one of the preceding claims, characterized by a pressure transducer p3 arranged in the first charge air pipe section (11) or in the charge air reservoir (10) for supplying a pressure value to the ECU. An internal combustion engine according to any one of the preceding claims, characterized by a pressure transducer p6 located in front of the SCR catalyst (20) in the second exhaust section (12) for supplying a pressure value to the ECU. An internal combustion engine according to any one of the preceding claims, characterized in that the control unit, after it has accumulated a plurality of sensor values, is used to pre-program the maps to control the operation of the heating devices and / or cooling devices. A method for controlling the operation of an internal combustion engine comprising an exhaust manifold (8) connected to the exhaust pipe, a charge air reservoir (10) attached to the charge air pipe, a high pressure turbocharger (2) with a high pressure turbine (3) and a low pressure turbocharger (5) is a low pressure turbine (6) and a low pressure compressor (7), an SCR catalyst (20) arranged between the high pressure turbine (3) and the low pressure turbine (6), the high pressure turbine (3) being in flow communication with the exhaust manifold (8) (6) via a second exhaust pipe section (12), the low pressure turbine (6) still in fluid communication with a third exhaust pipe section (13), the charge air pipe comprising a first charge air pipe section (11) between the charge air reservoir (10) and a high pressure compressor (4) 15) between the high pressure compressor (4) and the low pressure compressor (7), motor e delelle comprising means for influencing the exhaust gas temperature in the second exhaust section (12), characterized by: providing a first supercharger section (11), a second supercharger section (15) and / or a supercharger (10) for heating the exhaust gas in the second exhaust section (12) ) Upstream of the SCR catalytic converter (20), • determining the position of the charge air loss port (80, 82), • supplying the determined drive value to the control unit (ECU), • measuring the temperature te in the second exhaust section (12) upstream of the SCR catalyst (20). Supplying measured temperature values to the control unit (ECU), and controlling the charge air wastage port (80, 82) upstream of the SCR catalytic converter (20) to maintain the temperature within the desired range in the second exhaust section (12) of the SCR catalyst (20). upstream. A method according to claim 16, characterized by: • measuring the outdoor temperature, the charge air pressure pi after the intercooler (16) in the second charge air pipe section (15), the charge air pressure p3 in the charge air tank (10) or the first charge air pipe section (9); - after the turbine in the second exhaust section (12) and the engine load, and • supply the measured temperature, pressure and load values to the control unit. Method according to claim 16 or 17, characterized in that: • determining the position of the VIC, • entering the determined position values into the control unit. A method according to claim 17 or 18, characterized by: • determining the positions of the charge air bypass valve (24, 28, 34), the exhaust gas bypass valve (52, 62, 72) and the injection water valve (44, 46); . A method according to any one of claims 17 to 19, characterized by: • generating preprogrammed maps from values from different sources, and • using preprogrammed maps to control at least one of the following: a charge air bypass valve (24, 28, 34), an exhaust bypass valve (52, 62). , 72), a charge air bypass valve (80, 82) and an injection water valve (44, 46). Method according to Claim 16, characterized in that at least one of the following is controlled: a charge air bypass valve (24, 28, 34), an exhaust gas bypass valve (72), a charge air bypass valve (80, 82) and an injection water valve (44, 46) in the second exhaust section (12) upstream of the SCR catalyst (20). A method according to any one of claims 16 to 21, characterized in that the desired range of temperature te in the second exhaust section (12) upstream of the SCR catalyst (20) is about 350 ° C to 420 ° C.