GB2486734A

GB2486734A - Cooling re-circulated exhaust gases with engine coolant

Info

Publication number: GB2486734A
Application number: GB1021977.2A
Authority: GB
Inventors: Alberto Vassallo; David Giovanni
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2010-12-23
Filing date: 2010-12-23
Publication date: 2012-06-27
Anticipated expiration: 2030-12-23
Also published as: GB201021977D0; GB2486734B

Abstract

An internal combustion engine 10 comprising an engine coolant circuit 20 and an exhaust gas reÂcirculation (EGR) circuit 40, wherein the EGR circuit 40 comprises a first heat exchanger 33 and an auxiliary heat exchanger 42 which may exchange heat with an additional coolant circuit, and wherein the engine coolant circuit 20 comprises an electrically controlled valve 21 having an inlet 22 connected with a coolant outlet 14 of the engine 10, a first outlet 23 connected with a coolant inlet 15 of the engine 10 via a first line 24 and an engine coolant radiator 30, and a second outlet 25 connected with the coolant inlet 15 via a second line 26 which bypasses the first line 24 and radiator 30, and in which the first heat exchanger 33 is located, so as to allow an heat exchange between the coolant and the exhaust gas. Additionally a temperature parameter may be monitored and used to adjust the flow rate of the coolant routed to the first heat exchanger.

Description

INTERNAL (Xt4&JSTIC* ENGINE NO RELATED OPERATING METHQ)

TECHNICAL FIElD

The present invention relates to an internal corrthstion engine, espe- cially an internal combustion engine of a motor vehicle, and to a tie-thod for operating the same.

BAC2UND It is known that any kind of internal combustion engine, including Diesel engine, gasoline engine and gas engine, is conventionally equipped with an engine coolant circuit, in which a suitable engine coolant, typically a mixture of water and antifreeze, is circulated in order to cool the engine block and thus preventing overheating that can lead to engine malfunction.

This engine coolant circuit generally comprises a main pump for cir- culating the engine coolant, a radiator for cooling the engine coo-lant once it has passed through the engine block, and an auxiliary line for selectively bypassing the radiator during an early operating stage after the engine has been started, in order to speed up its warm-up.

The route of the engine' coolant is conventionally imposed by a ther-mostatic valve that forces the entire engine coolant to flow trough the auxiliary line until the temperature of the engine coolant is be-low a preset threshold, above which the thermostatic valve begins to progressively open also the connection with the engine coolant radia-tor.

Many internal cor±ustion engines are nowadays equipped also with an exhaust gas recirculation (EGR) circuit, which is provided for routing back the exhaust gas form the exhaust manifold to the intake manifold, principally in order to reduce the nitrogen oxides (NO) polluting emission.

Since the effectiveness of the NO reduction is heavily affected by the temperature of the recirculated exhaust gas, the EGR circuit con- ventionally comprises an heat exchanger, usually referred as EGR coo-ler, in which the heat of the recirculated exhaust gas is partially transferred to a proper coolant before reaching the intake manifold.

In order to improve the cooling of the recirculated exhaust gas, some EGR circuits, usually referred as low-temperature EGR circuit, fur-ther comprise an auxiliary heat exchanger located downstream of the EGR cooler, in which the recirculated exhaust gas is subjected to a second stage of cooling.

If not required, this second stage of cooling can be prevented by routing the exhaust gas in an line of the EGR circuit which bypasses the auxiliary heat exchanger.

In the auxiliary heat exchanger, the remaining heat of the recircu-lated exhaust gas is partially transferred to an additional coolant, typically a mixture of water and antifreeze, which circulates in an auxiliary coolant circuit separated from the engine coolant circuit described above.

Ps a consequence, this auxiliary coolant circuit generally comprises an auxiliary pump for circulating the coolant and an auxiliary radia- tor for cooling the coolant downstream of the auxiliary heat exchang-er.

The auxiliary radiator is usually realized in a dedicated portion of the engine coolant radiator, which is however hydraulically separated from the engine coolant circuit.

Conversely, for the sake of optimizing the thermal management of the engine, the first EGR cooler of the above named low-temperature EGR circuit can be connected with the engine coolant circuit, so that the first stage of cooling of the recirculated exhaust gas is effectively performed by the engine coolant.

Notwithstanding, this optimization finds an heavy limitation in the present desiqu of the engine coolant circuit, which does not allow a precise and effective control of the engine coolant circulation therein.

In view of the above, it is an object of an embodiment of the present invention to improve the thermal management cf an internal combustion engine, especially in order to achieve benefits in term NO emission reduction and fuel consumption.

Another object is to reduce NO emission while keeping hydrocarbon (HC) and carbon oxides (CO) emission within acceptable levels, and protecting vehicle driveability.

Still another object is to achieve the above mentioned objects with a simple, rational and rather inexpensive solution.

DISCLOSUEE

These and/or other objects are achieved by the features of the embo- diments of the invention as reported in independent claims. The de- pendent claims recite preferred and/or particularly advantageous fea-tures of the embodiments of the invention.

In greater detail, an embodiment of the invention provides an inter- nal combustion engine comprising an engine coolant circuit and an ex- haust gas recirculation circuit, wherein the exhaust gas recircula-tion circuit comprises a first heat exchanger and an auxiliary heat exchanger, and wherein the engine coolant circuit comprises an elec-trically controlled valve having an inlet connected with a coolant outlet of the engine, a first outlet connected with a coolant inlet of the engine via a first line in which an engine coolant radiator is located, and a second outlet connected with the coolant inlet of the engine via a second line which bypasses the first line and in which the first heat exchanger is located, so as to allow an heat exchange between the engine coolant and the recirculated exhaust gas.

Thanks to the electrically controlled valve, it is advantageously possible to control the circulation of the engine coolant in the en- gine coolant circuit at will, so as to optimize the thermal manage-ment of the engine at any stage of the engine operation and under any operating condition.

According to an aspect of the invention, the engine coolant circuit comprises a second heat exchanger, which is located in the second line downstream of the first heat exchanger and which is connected with an engine lubrication circuit, so as allow an heat exchange be-tween engine coolant and engine lubricant.

This solution advantageously allows to heat the engine lubricant us-ing the engine coolant that has been heated in turn by the exhaust gas, which can mainly contribute in reducing frictions and thus fuel consi.nnption during engine warm-up.

According to another aspect of the invention, the engine coolant cir-cuit comprises an heater core located in a third line that connects a third outlet of the valve with the coolant inlet of the engine, by-passing the first line and the second line.

In this way, by means of the electrically controlled valve is advan-tageously possible to properly manage also the heating of the cabin of the motor vehicle.

According to still another aspect of the invention, the exhaust gas recirculation circuit comprises a line bypassing the auxiliary heat exchanger, and electrically controlled means for regulating the flow rate of exhaust gas that flows trough this bypassing line and the flow rate of exhaust gas that flows through the auxiliary heat ex-changer.

By way of example, these electrically controlled means can comprise a valve for selectively opening and closing the above named bypassing line.

With this solution it is advantageously possible to selectively al-lowing or preventing the recirculated exhaust gas to flow through the auxiliary heat exchanger, thereby achieving a better control on the engine polluting emission.

Another embodiment of the invention provides a method for operating an internal cortbustion engine, specially an internal combustion en-gine of the kind described above.

The operating method generally involves several alternative operating modes, which are performed while the internal combustion engine is actually operating.

More particularly, the method comprises a normal operating mode com-prising the steps of: -routing back exhaust gas from an exhaust manifold to an intake manifold of the engine, -circulating engine coolant in an engine coolant circuit, -routing at least part of the engine coolant to exchange heat with the recirculated exhaust gas, -routing the exhaust gas to exchange heat with an additional coolant, -monitoring a paraireter related to the temperature of the engine coolant, -determining a setpoint value of this parameter, -adjusting the flow rate of the part of engine coolant routed to exchange heat with the recirculated exhaust gas, so as to mi-nimize an error between a monitored value of the said parameter and the setpoint value.

This normal mode can be advantageously performed once the internal cortustion engine is properly warmed-up, and it provides a reliable feedback control of the engine coolant temperature, which can there-fore effectively respond to any variation of the engine operating conditions.

According to an aspect of the invention, the method further comprises a warm-up operating mode providing that the whole engine coolant is constantly routed to exchange heat with the recirculated exhaust gas.

This warm-up mode can be advantageously performed before the above mentioned normal mode, and it allows the recirculated exhaust gas to heat the engine coolant thereby guiokening the engine warm-up.

In particular, an aspect of the warm-up operating mode provides that the engine coolant is also routed to exchange heat with an engine lu-brioarit.

In this way, the engine coolant heated by the recirculated exhaust gas is advantageously used for heating the engine lubricant, thereby reducing the frictions and thus the fuel consumption during the en-gine warm-up.

According to another aspect of the invention, the method further com-prises the steps of: -monitoring an engine operating parameter, and -switching from the warm-up operating mode to the normal operat-ing mode if a monitored value of the engine operating parameter exceeds a threshold value of this engine operating parameter.

In this way, it is advantageously possible to trigger the normal op- erating mode as soon as it is advisable to do so, in order to optim-ize the thermal management of the engine.

As a matter of fact, the above named engine operating parameter can be chosen among: engine speed, engine load, an engine operating time and any engine parameter related to the engine temperature, such as for example engine coolant temperature at the engine coolant outlet or engine bulk temperature.

According to another aspect of the invention, the method further corn-prises the steps of: -monitoring an engine operating parameter, typically engine speed, engine load or engine torque, and -preventing the exhaust gas to exchange heat with the additional coolant until a monitored value of the engine operating parame- ter exceeds a threshold value of this engine operating pararre-ter.

These steps can be advantageously performed, specially during the warm-up mode and/or of the normal mode, in order to reduce the NO emission while keeping 00 and HO emissions within acceptable levels.

According to still another aspect of the invention, the method fur- ther involves an early stage operating mode providing that the circu-lation of engine coolant in the engine coolant circuit is constantly prevented.

This early stage mode can be advantageously performed before the

S

warn-up stage operating mode1 for it allows to quicker the heating of the cylinder head when the engine is very cold just after the start.

An aspect of the early stage operating mode provides that the exhaust gas is constantly prevented to exchange heat with the additional coo-lant.

In this stage there is indeed no need of overcooling the recirculated exhaust gas, which is therefore prevented to exchange heat with the additional coolant.

According to another aspect of the invention, the method further com-prises the steps of: monitoring an engine operating parameter, and -switching from the early stage operating mode and the warn-up operating mode if a monitored value of the engine operating pa- rameter exceeds a threshold value of this engine operating pa-rameter.

In this way, it is advantageously possible to trigger the warn-up op- erating mode as soon as it is advisable to do so, in order to optim-ize the thermal management of the engine.

Also in this case, the above named engine operating parameter can be chosen among: engine speed, engine load, an engine operating tine and any engine parameter related to the engine temperature, such as for example engine coolant temperature at the engine coolant outlet or engine bulk temperature.

The operating method according to the invention can be carried out with the help of a computer program comprising a program-code for carrying out the method described above, and in the form of a conput-er program product ccrnprising the computer program.

By way of example, the computer program product can be embodied as a control system for an internal combustion engine, comprising an en-gine control unit (ECU), a data carrier associated to the ECU, and the computer program stored in the data carrier, so that, when the ECU executes the computer program, the method described above is car-ried out.

The method could be also embodied as an electraTlagnetic signal, said signal being modulated to carry a sequence of data bits which represent a computer program to carry out the method.

BRIEF DESRIPTI4 OF ThE DRPWINGS The present invention will now be described, by way of example, with reference to the acccrnpanying drawings.

Figure 1 is a scheme of an internal ccxnbustion engine of a motor ve-hicle.

Figure 2 is a flowchart of a method for operating the internal corn-bustion engine of figure 1.

Figure 3 is a flowchart of a strategy for controlling the engine coo-lant circuit during a normal operating mode of the method of figure 2.

Figure 4 is a flowchart of a strategy for controlling the EGR circuit during a warm-up operating mode and a normal operating mode of the method of figure 2.

DEThILED DESCRIPTflI The present embodiment of the invention is hereinafter described re-ferring to a Diesel engine 10, but it could also be applied to other kind of internal combustion engines, such as for example a gasoline engine.

The Diesel engine 10 essentially comprises an intake manifold 11 for feeding fresh air fran the environment into the engine cylinders 12, fuel injectors (not shown) for injecting fuel into the engine cylind-ers 12 so as to trigger the combustion, and an exhaust manifold 13 for discharging exhaust gas from the engine cylinders 12 to the envi-ronment.

The Diesel engine 10 is equipped with an engine coolant circuit, glo-bally indicated as 20, in which a suitable engine coolant, typically a mixture of water and antifreeze, is circulated in order to cool the engine block and other engine components, thereby preventing over-heating that can lead to engine malfunction.

The engine coolant circuit 20 comprises an electrically driven pro-portional valve 21 having an inlet 22 connected with a coolant outlet 14 of the Diesel engine 10, a first outlet 23 connected with a coo-lant inlet 15 of the Diesel engine 10 via a first line 24, a second outlet 25 connected with the coolant inlet 15 of the Diesel engine 10 via a second line 26 which bypasses the first line 24, and a third outlet 27 connected with the same ccolant inlet 15 of the Diesel en-gine 10 via a third line 28 which bypasses both the first line 24 and the second line 26.

The valve 21 is also provided with a movable member (not shown) which is suitable for selectively closing, opening and also regulating the opening degree of each outlets 23, 25 and 27.

S The valve 21 is wired to an engine control unit (ECU) 100, which con-trols the operation of the valve 21 so as to properly move the above named movable member, thereby regulating the flow rate of engine coo-lant that flows in the fist line 24, the second line 26 and/or the third line 28.

The circulation of the engine coolant in the engine coolant circuit is caused by a coolant pump 29, which is driven by the Diesel en-gine 10, and through which the first line 24, the second line 26 and the third line 28 are individually connected with the coolant inlet of the Diesel engine 10.

The first line 24 is provided with an engine coolant radiator 30 suitable for cooling the engine coolant once it has passed through the Diesel engine 10.

This engine coolant radiator 30 is a liguid-air heat exchanger, which is often located in the rear part of the motor vehicle, and which is generally associated with a fan (not shown) that blows air through it in order to improve the efficiency of the heat exchange between en-gine coolant and air.

The third line 28 is provided with an heater core 31, which is a ra-diator-like device used for heating the cabin of the motor vehicle, and with an electrically driven auxiliary pump 32 located between the valve 21 and the heater core 31.

Finally, the second line 26 is provided with a first heat exchanger 33 and with a second heat exchanger 34 located downstream of the first one.

S The second heat exchanger 34 is connected with a conventional engine lubricaticn circuit 50 (not shown in detail), in which an engine lu- bricant, usually oil, is circulated in order to lubricate the rotat-ing or sliding components of the Diesel engine 10.

The second heat exchanger 34 is therefore suitable for exchanging heat between engine coolant and engine lubricant.

The first heat exchanger 33 is connected to an exhaust gas recircula-tion (EGR) circuit 40 of the Diesel engine 10, which is provided for routing back the exhaust gas form the exhaust manifold 13 to the in-take manifold 11, with the aim of reducing the nitrogen oxides (NO) polluting emission.

In this way, the first heat exchanger 33 is suitable for exchanging heat between the recirculated exhaust gas and the engine coolant, principally in order to cool the recirculated exhaust gas before it reaches the intake manifold 11, so as to increase the NO reduction efficiency.

In greater detail, the EGR circuit 40 of the present embodiment of the invention is a low-temperature EGR circuit, which comprises a main line 41 connecting the exhaust manifold 13 with the intake mani-fold 11, the already mentioned first heat exchanger 33 located in the main line 41, and also an auxiliary heat exchanger 42 located in the main line 41 downstream of the first heat exchanger 33, so that the recirculated exhaust gas can be subjected to a second stage of cool-ing.

In the auxiliary heat exchanger 42, the remaining heat of the recir- culated exhaust gas is partially transferred to an additional coo-lant, typically a mixture of water and antifreeze, which circulates in an auxiliary coolant circuit 60 separated from the engine coolant circuit 20 described above.

In addition to the auxiliary heat exchanger 42, the auxiliary coolant circuit 60 further canprises an electrically driven pump 61 for cir-culating the additional coolant, whose operation is controlled by the ECU 100, and an auxiliary radiator 62 for cooling the coolant down-stream of the auxiliary heat exchanger 42.

The auxiliary radiator 62 is realized in a dedicated portion of the engine coolant radiator 30, which is however hydraulically separated from the engine coolant circuit 20.

The EGR circuit 40 further carprises a line 43, which connects the exhaust gas outlet of the first heat exchanger 33 with the intake ma- nifold 11 bypassing the auxiliary heat exchanger 42, and an electri-cally controlled ON-OFF valve 44 located in the bypassing line 43 for selectively opening or closing the same, which is controlled by the ECU 100.

More particularly, the ECU 100 controls the whole operation of the Diesel engine 10 by implementing the method that is schematically shown in figure 2.

This operating method generally comprises several alternative operat-ing mode, which are performed consecutively from the instant in which the Diesel engine 10 is started.

The first operating mode is a so called degassing mode, which is suitable for removing the gas that can be present in the engine coo-lant after a certain period of inactivity.

This degassing mode generally provides for acting the movable member of the valve 21 in a full travel between a first position, in which the engine coolant does not circulate in the circuit 20, and a second position, in which the engine coolant is entirely routed towards the engine coolant radiator 30.

While performing the degassing mode, the valve 44 of the EGR circuit is kept open, while the electrically driven pump 61 is constantly kept off by default.

The duration of this degassing mode can be determined by means of a calibration activity and it is stored in a data carrier 101 asso-ciated with the ECU 100.

Generally the degassing mode lasts about ten seconds from the start of the Diesel engine 10.

The degassing mode is followed by an early stage operating mode, also referred as zero-flow mode, during which the movable member of the valve 21 is constantly kept in a position such that the circulation of the engine coolant in the engine coolant circuit 20 is prevented.

This early stage mode advantageously allows a quicker heating of the cylinder head when the Diesel engine 10 is still cold just after the start.

In this early stage operating mode there is no need of overcooling the recirculated exhaust gas.

Accordingly, the early stage mode provides for keeping the valve 44 of the EGR circuit 40 constantly open, while the electrically driven pump El is constantly kept off by default, in order to save energy.

The duration of the early stage operating mode is variable and it is determined by monitoring an engine operating parantter, which can be measured by means of dedicated sensor or estimated, and by comparing its value EOP1 with a predetermined threshold value TV1, which is stored in the data carrier 101.

The threshold value TV1 can be empirically determined during a cali-bration activity.

The above named engine operating parameter can be for example engine speed, engine load, an engine operating time (including for instance the time period from the start of the Diesel engine 10 or the time period from the beginning of the early stage operating mode) or a pa-raineter related to the temperature of the Diesel engine 10, including for example the engine coolant temperature at the engine coolant out-let 14 or the engine bulk temperature.

If the monitored value EOP1 of this engine operating parameter ex-ceeds the threshold value TV1 related thereto, the operating method provides for switching from the early stage operating mode to a warm-up operating mode.

This warm-up operating mode provides that the engine coolant is con-stantly prevented to flow through the first line 24 and routed only through the second line 26.

In this way, the engine coolant is heated by the recirculated exhaust gas in the first heat exchanger 33, and then it is used for heating the engine lubricant in the second heat exchanger 34, which fluidi-lies quickly, thereby reducing frictions between the rotating and/or sliding ccrnponents of the Diesel engine 10 and thus the fuel consurrip-tion during the engine warm-up.

Also the duration of the warm-up operating mode is variable and it is determined by monitoring an engine operating pararreter, which can be measured by means of dedicated sensor or estimated, and by ccmparing its value EOP2 with a predetermined threshold value TV2, which is stored in the data carrier 101.

The threshold value 1V2 can be empirically determined during a cali-bration activity.

The engine operating parameter here concerned can be the same that has been used for determining the ending of the early stage operating mode, but it can also be different.

Leastways, the engine operating parameter can be chosen for example among: engine speed, engine load, an engine operating time (including for instance the time period from the start of the Diesel engine 10 or the time period fran the beginning of warm-up operating mode) or a parameter related to the temperature of the Diesel engine 10, includ-ing for example the engine coolant temperature at the engine coolant outlet 14 or the engine bulk temperature.

If the monitored value EOP2 of this engine operating parameter ex-ceeds the threshold value TV2 related thereto, the operating strategy provides for switching from the warm-up operating mode to a normal operating mode.

Obviously, the threshold value TV2 here concerned should be higher than the threshold value T\Jl involved in determining the ending of the early stage operating mode.

The above named normal operating mode is advantageously performed once the internal combustion engine is properly warmed-up, and it generally provides a feedback control of the engine coolant tempera-ture, which can therefore effectively respond to any variation of the engine operating conditions.

As shown in figure 3, this feedback control comprises the essential steps of: -monitoring, by means of a dedicated sensor or estimation, a pa-rameter related to the temperature of the engine coolant, such as for example the engine coolant temperature at the engine coolant outlet 14 or the engine bulk temperature, -determining a setpoint value CT_tar of this parameter, for ex-ample through an empirically calibrated map stored in the data carrier 101 associated with the ECU 100, -calculating an error E (namely the difference) between the set point value CT_tar and the monitored value CT_mon of the para-meter, and then -applying this error E to a controller, for example a propor-tional integrative (P1) controller, which affects the position of the movable member of the valve 21, in order to adjust the ratio between the flow rate of engine coolant flowing through the first line 24 and the flow rate of engine coolant flowing through the second line 26, 50 as to minimize the above named error E. As a matter of fact, the conventional transfer function of a P1 con-troller is: Y(t) = K E(t) + K, Je(r)dr wherein: Y(t) is the output of the controller, such as for example the angular position of the movable member of the valve 21, E(t) is the error, r is a dummy integration variable, �^ç is the proportional gain, and K1 is the integrative gain.

The proportional gain K, and the integrative gain K1 are predetermined and stored in the data carrier 101.

However, the normal operating mode provides that, if the error E ex- ceeds a given safety threshold value of the error itself, the propor-tional gain iç and the integrative gain K1 will be corrected so as to increasing the proportional term of the transfer function and de-creasing the integral one.

This feature advantageously allows to restore the feedback control in critical conditions.

The output Y generated by the controller is finally filtered, for ex-ample with a first order filter, whose time constant is calibratable, and then it is converted from degrees to an electrical control signal (volts) arid supplied to the valve 21.

The normal operating mode can also involve a feedback control of the position of the movable merriber of the valve 21, by means of a posi- tion sensor that generated an electrical signal related to the posi-tion of the movable merter, which is then converted into degrees by the controller.

Furthermore, the normal operating mode comprises also a strategy to diagnose the failure of the tracking control signal, which generally provides that a failure will be identified, if the error F remains greater than a predetermined threshold value beyond a determined threshold time.

As shown in figure 2, at the same time in which the warn-up operating mode is triggered, a control strategy of the EGR circuit 40 is also enabled.

As shown in figure 4, this control strategy provides that the electr-ically driven pump 61 of the auxiliary coolant circuit 60 is turned on, and that it is constantly kept on, during both the warn-up oper-ating mode and the normal operating mode, that is until the Diesel engine 10 is stopped by turning the key off.

While the pump 61 is working, the strategy generally provides for controlling the valve 44 by monitoring an engine operating pararreter, which can be measured by means of a dedicated sensor or estimated, and by ccrnparing its value EOP3 with a predetermined threshold value TV3, which is stored in the data carrier 101 associated with the ECU 100.

The threshold value TV3 can be empirically deteirnined during a cali-bration activity.

In this case, the engine operating parameter can be chosen among en-gine speed, engine load and engine torque.

Mere particularly, as long as the monitored value EOP3 of the engine operating parameter is below the threshold value TV3 related thereto, the valve 44 is kept open, so that the recirculated exhaust gas flows entirely through the line 43 bypassing the auxiliary heat exchanger 42.

If the monitored value E0P3 of the engine operating parameter exceeds the above named threshold TV3, the valve 44 is closed and kept closed for a certain time period, routing the whole recirculated exhaust gas trough the auxiliary heat exchanger 42.

In this way, the recirculated exhaust gas is subjected to a second stage of cooling, which allows to further reduce the NQ polluting emission.

Contemporaneously, the operating strategy provides also to monitor the arrtient temperature and to keep the valve 44 constantly open as long as the monitored value T of the ambient temperature falls out a predetermined range of values between two calibratable threshold val-ues TI and T2, for example if the monitored value T is smaller than 19°C or greater than 30°C.

During all the operating modes described above, the valve 21 is fur-ther controlled in order to selectively route into the third line 28 a controlled flow rate of engine coolant, if an heating of the cabin is required.

In this case, the above mentioned threshold values and setpoint val- ues can be corrected, in order to take into account the heat dissi-pated by the engine coolant in the heater core 31.

While at least one exemplary embodiment has been presented in the foregoing surrmary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only exam- ples, and are not intended to limit the scope, applicability, or con- figuration in any way. Rather, the forgoing suirmary and detailed de-scription will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and ar-rangement of elements described in an exemplary embodirrent without departing from the scope as set forth in the appended claims and in their legal equivalents.

REFERENCES

Internal combustion engine 11 Intake manitold 12 Engine cylinder 13 Exhaust manifold 14 Engine coolant outlet Engine coolant inlet Engine coolant circuit 21 Valve 22 Valve inlet 23 First valve outlet 24 First line Second valve outlet 26 Second line 27 Third valve outlet 28 Third line 29 Coolant purrq Engine coolant radiator 31 Heater core 32 Auxiliary purrp 33 First heat exchanger 34 Second heat exchanger Exhaust gas recirculation (EGR) circuit 41 Main line 42 Auxiliary heat exchanger 43 Line 44 Valve Engine lubrication circuit Auxiliary coolant circuit 61 Pump 62 Auxiliary radiator Engine control unit (ECU) 101 Data carrier EOP1 Value of an engine operating parameter TV1 Threshold value EOP2 Value of an engine operating parameter TV2 Threshold value EOP3 Value of an engine operating parameter TV3 Threshold value CT tar Setpoint value of a coolant temperature parameter E error CT_mon Monitored value of the coolant temperature pararreter T Monitored value of the ambient temperature Ti Threshold value of the ambient temperature T2 Threshold value of the ambient temperature

Claims

1. An internal combustion engine (10) comprising an engine coolant circuit (20) and an exhaust gas recirculation circuit (40), wherein the exhaust gas recirculation circuit (40) comprises a first heat exchanger (33) and an auxiliary heat exchanger (42), and wherein the engine coolant circuit (20) comprises an electri-cally controlled valve (21) having an inlet (22) connected with a coolant outlet (14) of the engine (10), a first outlet (23) con-nected with a coolant inlet (15) of the engine (10) via a first line (24) in which an engine coolant radiator (30) is located, and a second outlet (25) connected with the coolant inlet (15) of the engine (10) via a second line (26) which bypasses the first line (24) and in which the first heat exchanger (33) is located, so as to allow an heat exchange between the engine coolant and the recirculated exhaust gas.

2. un internal combustion engine (10) according to claim 1, wherein the engine coolant circuit (20) comprises a second heat exchanger (34), which is located in the second line (26) downstream of the first heat exchanger (33) and which is connected with an engine lubrication circuit (50), so as allow an heat exchange between engine coolant and engine lubricant.

3. An internal combustion engine (10) according to any of the pre-ceding claims, wherein the engine coolant circuit (20) comprises an heater core (31) located in a third line (28) that connects a third outlet (27) of the valve (21) with the coolant inlet (15) of the engine (10), bypassing the first line (24) and the second line (26).

4. An internal canbustion engine (10) according to any of the pre-ceding claims, wherein the exhaust gas recirculation circuit (40) comprises a line (43) bypassing the auxiliary heat exchanger (42), and electrically controlled means (44) for regulating the flow rate of exhaust gas that flows trough this bypassing line (43) and the flow rate of exhaust gas that flows through the aux-iliary heat exchanger (42).

5. A method. for operating an internal combustion engine (10) com-prising a normal operating mode which comprises the steps of: -routing back exhaust gas from an exhaust manifold (13) to an intake manifold (11) of the engine (10), -circulating engine coolant in an engine coolant circuit (20), -routing at least part of the engine coolant to exchange heat with the recirculated exhaust gas, -routing the exhaust gas to exchange heat with an additional coolant, -monitoring a pararreter related to the temperature of the en-gine coolant, -determining a setpoint value (CT_tar) of this parameter, -adjusting the flow rate of the part of engine coolant routed to exchange heat with the recirculated exhaust gas, so as to minimize an error (E) between a monitored value (CTmon) of the said parameter and the setpoint value (CT_tar).

6. A method according to claim 5, comprising a warm-up operating mode providing that the whole engine coolant is constantly routed to exchange heat with the recirculated exhaust gas.

7. A method according to claim 6, wherein the warm-up operating mode provides that the engine coolant is routed to exchange heat with an engine lubricant.

8. A method according to any claim from 6 to 7, comprising the steps of: -monitoring an engine operating parameter, and -switching from the warn-up operating mode and the normal op- erating mode if a monitored value (EOP2) of the engine oper- ating parameter exceeds a threshold value (TV2) of this en-gine operating parameter.

9. A method according to any claim from claim 5 to 8, comprising the steps of: -monitoring an engine operating parameter, -preventing the exhaust gas to exchange heat with the addi-tional coolant until a monitored value (EOP3) of the engine operating parameter exceeds a threshold value (TV3) of this engine operating parameter.

10. A method according to any claim from 5 to 9, comprising an early stage operating mode providing that the circulation of engine coolant in the engine coolant circuit (20) is constantly pre-vented.

11. A method according to claim 10, wherein the early stage operating node provides that the exhaust gas is constantly prevented to ex-change heat with the additional coolant.

12. A method according to any claim from 10 to 11, comprising the step of: -monitoring an engine operating parameter, and -switching from the early stage operating mode and the warm-up mode if a monitored value (EOP1) of the engine operating parameter exceeds a threshold value (IV1) of this engine op-erating parameter.

13. A method according to claim 8 or 12, wherein the engine operating parameter is chosen among: engine speed, engine load, any engine parameter related to the engine tertperature and an engine operat-ing time.

14. A computer program comprising a computer-code for performing the method according to any claim from 5 to 13.

15. Computer program product on which the computer program according to claim 14 is stored.