GB2480824A - Internal combustion engine with an exhaust gas recirculation system having a bypass conduit - Google Patents

Abstract

Internal combustion engine 1 with an intake manifold 2, an exhaust manifold 3, a lubricating circuit 4 and an exhaust gas recirculation system 5, EGR, where the EGR system comprises a main conduit 50 connecting the exhaust and intake manifolds, a cooler 51, a bypass conduit 52 to bypass the cooler and a first valve 53 for alternatively routing the exhaust gas through the cooler or the bypass conduit, where there is a heat exchanger 6 in the bypass conduit that is connected to the lubricating circuit. A second valve 62, which may be a flow rate control valve, may be located in a conduit 60 connecting the heat exchanger with the lubricating circuit, where both of the valves are connected to an engine control unit, ECU. A method for operating an internal combustion engine is also claimed.

Description

INTERNAL CCMBUSTION ENGINE

TECHNICAL FIElD

The present invention relates to an internal combustion engine, typi- cally an internal combustion engine of a motor vehicle, which is pro-vided with an exhaust gas recirculation system and with a lubricating circuit.

BA

n internal combustion engine is conventionally provided with an in-take manifold, an exhaust manifold, an intake line for conveying fresh air from the environment into the intake manifold, and an ex-haust line for conveying the exhaust gas from the exhaust manifold to the environment.

In order to reduce the polluting emission, most internal combustion engines, principally Diesel engines, are further equipped with an ex-haust gas recirculation (EGR) system, for selectively routing back a part of the exhaust gas from the exhaust manifold into the intake ma-nifold.

Conventional EGR systems caiiprise an EGR conduit, also known as high pressure EGR conduit or short-route EGR conduit, which fluidly con-nects the exhaust manifold with the intake manifold, an EGR cooler for cooling the exhaust gas before mixing it with the induction air, and a valve for regulating the flow rate of exhaust gas in the EGR conduit.

1⁄2n Electronic Control Unit (ECU) based on a microprocessor is conven-tionally provided for determining the required amount of exhaust gas to be recirculated, and for controlling the above mentioned valve ac-cordingly.

In this way, a part of the exhaust gas is mixed with the fresh induc-tion air and is fed into the engine cylinders, thereby reducing the production of oxides of nitrogen (NO) during the combustion processed.

Nonetheless, the antipollution effect of the EGR system is strongly reduced if the temperature of the recirculated exhaust gas is too cold, such as for example at the start of the engine, to the point that an overcooled exhaust gas can even deteriorate the combustion process.

For this reason, in order to quicken the warm-up of the exhaust gas at the start of the engine, the EGR systems further comprises a by-pass conduit, connected in parallel to the EGR cooler, and another valve for selectively routing the exhaust gas in the bypass conduit, thereby preventing the recirculated exhaust gas to be cooled inside the EGR cooler.

However, the exhaust gas is not the only engine fluid whose efficien-cy depends on its temperature.

Another engine fluid having this problem is the lubricating oil that circulates in the lubricating circuit of the internal combustion en-gine, for lubricating and cooling the rotating or sliding components of the engine.

In fact, the efficiency of the lubricating oil depends on its viscos- ity, which in turn is strongly affected by the temperature of the lu-bricating oil.

As a consequence, at the start of the engine, when the lubricating oil is cold, it has a great viscosity that increases the engine fric- tions, thereby causing an increased fuel consumption in this operat-ing phase.

An object of an embodiment of the present invention is therefore to quicken the warm-up of the lubricating oil in the lubricating cir-cuit, so as to achieve a better oil viscosity that lead to a better fuel economy.

Another object is to meet this goal by means of a simple, rational and low cost solution.

These and/or other objects are attained by the characteristics of the embodiments of the invention as reported in independent claims. The dependent claims recite preferred and/or especially advantageous fea-tures of the embodiments of the invention.

SRY

An embodiment of the invention provides an internal combustion engine equipped with an intake manifold, an exhaust manifold, a lubricating circuit and an exhaust gas recirculation system.

The exhaust gas recirculation system comprises a main conduit that fluidly connects the exhaust manifold with the intake manifold, a cooler located in the main conduit, a bypass conduit connected with the main conduit so as to bypass the cooler, and a first valve for alternatively routing the exhaust gas from the exhaust manifold to-wards the cooler or towards the bypass conduit.

According to the present embodiment of the invention, an heat ex- changer is located in the bypass conduit and is connected to the lu-bricating circuit.

This solution advantageously allows to use the heat of the exhaust gas, in order to quicken the warm-up of the lubricating oil at the start of the engine, thereby reducing the engine frictions and the fuel consumption.

According to an aspect of the invention, a second valve, for example an on-off valve or eventually a flow rate control valve, is located in a conduit connecting the heat exchanger with the lubricating cir-cuit.

This feature allows to regulate the flow rate of lubricating oil that flows through the heat exchanger, thereby controlling the heat that is effectively exchanged between the exhaust gas and the lubricating oil.

According to another aspect of the invention, the first valve and the second valve are connected to an engine control unit.

This aspect provides a simple way to control the first valve and the second valve, during the operation of the internal combustion engine.

According to still another aspect of the invention, the cooler and the heat exchanger have a common external housing.

This aspect has the advantage of allowing an economic and compact realization of both the cooler and the heat exchanger, thereby reduc-ing the cost and the packaging issues inside the engine compartment of the vehicle.

Pn embodiment of the invention further provides a method for operat-ing the above disclosed internal combustion engine, which comprises the steps of: -monitoring an actual value of a parameter correlated with an engine temperature, -routing exhaust gas from the exhaust manifold towards the heat ex-changer, if the actual value of the parameter is lower than a first threshold value of the parameter, -routing the exhaust gas from the exhaust manifold towards the coo-ler, if the actual value of the parameter is equal or greater than the first threshold value of the parameter.

By a proper calibration of the first threshold value, this solution forces the exhaust gas to pass through the heat exchanger, when the engine temperature is low, in order to quicken the warm-up of the ex-haust gas itself and of the lubricating oil, and to pass through the cooler, when the engine temperature reaches a value for which the ex-haust gas and the lubricating oil are sufficiently warm.

According to an aspect of the invention, the method comprises the further steps of: -preventing lubricating oil to flow through the heat exchanger, if the actual value of the parameter is lower than a second threshold value of the parameter, -allowing lubricating oil to flow through the heat exchanger, if the actual value of the parameter is equal or greater than the second threshold value of the parameter, the second threshold value being lower than the above mentioned first threshold value.

This aspect of the invention advantageously allows to reduce the heat exchange between the exhaust gas and the lubricating oil, when the engine is very cold, in order to not overcooling the exhaust gas, de-teriorating the combustion processes.

According to another aspect of the invention, the method comprises the further step of modulating the flow rate of lubricating oil flow-ing through the heat exchanger, if the actual value of the parameter is comprised between the first threshold value and the second thre-shold value.

This solution advantageously allows to regulate the quantity of heat that is effectively exchanged between the exhaust gas and the lubri-cating oil.

According to still another aspect of the invention, the above men- tioned parameter is chosen from engine coolant temperature, lubricat-ing oil temperature, and exhaust gas temperature.

This parameters are strictly correlated with the engine temperature and their values are generally already available for other purposes, so that this aspect of the invention provides a very simple and eco-nornic solution for monitoring the engine temperature.

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

The computer program product can be embodied as control apparatus for an internal combustion engine comprising an ECU, a data carrier asso- ciated to the ECU, and the computer program stored in the data carri-er, so that, when the ECU executes the computer program, all the steps of the method described above are carried out.

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

BRIEF DESCRIPTIC*1 OF T! DRAWINGS The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: figure 1 schematically illustrates an internal combustion engine pro-vided with an exhaust gas recirculation system and a lubricating oil circuit according to an embodiment of the invention; figure 2 schematically illustrates a specific configuration of a coo- ler and an heat exchanger of the exhaust gas recirculation system ac-cording to an embodiment of the invention; figure 3 is a flowchart schematically representing a strategy for op-erating the internal combustion engine of figure 1.

DETAILED DESCRIPTI4 OF THE DRAWINGS Figure 1 shows an internal combustion engine 1 of a motor vehicle, in this case a Diesel engine.

The internal combustion engine 1 has an intake manifold 2 and an ex-haust manifold 3.

The intake manifold 2 is conventionally connected with an intake line (not shown) for conveying fresh air from the environment into the in-ternal combustion engine 1.

The exhaust manifold 3 is conventionally connected with an exhaust line (not shown) for conveying the exhaust gas from the internal com-bustion engine 1 to the environment.

The internal combustion engine 1 is equipped with a conventional lu-bricating circuit 4 (represented in dotted line in figure 1), in which a lubricating oil is circulated so as to cool and lubricate the rotating or sliding components of the internal combustion engine 1, such as for example crankshaft bearings (main bearings and big-end bearings), camshaft bearings operating the valves, tappets, and the like.

In order to reduce the emission of nitrogen oxides (NO), the internal combustion engine 1 is further equipped with an exhaust gas recircu-lation (EGR) system, globally indicated as 5, which is provided for routing back and feeding exhaust gas into the internal combustion en-gine.

The EGR system 5 comprises an main conduit 50, generally referred as short-route EGR conduit or high pressure EGR conduit, which fluidly connects the exhaust manifold 3 directly with the intake manifold 2, and a cooler 51, generally referred as EGR cooler, which is located in the main conduit 50, for cooling the exhaust gas flowing therein.

The cooler 51 is a conventional heat exchanger, by means of which the exhaust gas flowing in the main conduit 50 is cooled by an engine coolant, typically water.

In greater details, the cooler 51 comprises an external casing 510 defining an internal chamber 511 for the exhaust gas, and a tube bun-dle 512, located inside the internal chamber 511.

The tube bundle 512 has an inlet and an outlet leading outside the external casing 510, which are hydraulically connected to a circuit of the engine coolant, so that the engine coolant can flow through the cooler 51.

In this way, the cooler 51 allows the engine coolant to cool the ex-haust gas, keeping them physically separated.

The EGR system 5 further comprises a bypass conduit 52 connecting a first point of the main conduit 50, located upstream the cooler 51, with a second point of the main conduit 50, located downstream the cooler 51.

As a matter of fact, the bypass conduit 52 is connected in parallel to the cooler 51.

A valve 53 is located in the above mentioned first point of the main conduit 50, for alternatively routing the exhaust gas coming from the exhaust manifold 3 towards the cooler 51 or towards the bypass con-duit 52.

Another valve 54 is located in the main conduit 50 upstream the valve 53, in order to regulate the flow rate of exhaust gas that is global-ly routed back from the exhaust manifold 3 to the intake manifold 2.

According to an embodiment of the invention, an heat exchanger 6 is located in the bypass conduit 52.

The heat exchanger 6 is hydraulically connected with the lubricating circuit 4, so that the lubricating oil can flow through the heat ex-changer 6.

In greater details, the heat exchanger 6 comprises an external casing 600 defining an internal chamber 601 for the exhaust gas, and a tube bundle 602 located inside the internal chamber 601.

The tube bundle 602 has an inlet and an outlet leading outside the external casing 600.

The inlet of the tube bundle 602 is hydraulically connected to the lubricating circuit 4 by means of a feeding conduit 60, which routes the lubricating oil from the lubricating circuit 4 into the heat ex-changer 6.

The outlet of the tube bundle 602 is hydraulically connected to the lubricating circuit 4 by means of a discharging conduit 61, which routes back the lubricating oil from the heat exchanger 6 again into the lubricating circuit 4.

In this way, the heat exchanger 6 allows the exhaust gas to heat the lubricating oil, keeping them physically separated.

A valve 62 is located in the feeding conduit 60, in order to regulate the flow rate of lubricating oil that flows through the heat exchang- er 6, thereby controlling the heat that is effectively exchanged be-tween the exhaust gas and the lubricating oil.

In the present exanle, the valve 62 is an on-off valve, which allows or prevent the lubricating oil to flow through the heat exchanger 6.

However, the valve 62 could be a flow rate control valve, namely a valve configured so as to be able to modulate the flow rate of lubri-cating oil which flows through the feeding conduit 60.

In the alternative embodiment shown in figure 2, the heat exchanger 6 is closed coupled with the cooler 51, so as to globally realize a single component.

In greater details, this single component comprises a common external casing 603 and an internal wall 604, which divides the internal vo-lume of the common casing 603 in two separated chambers, including a first chamber 605 located in the main conduit 50, and a second cham-ber 606 located in the bypass conduit 52.

The first chamber 605 accommodates the tube bundle 512, so as to realize the cooler in which the exhaust gas is cooled by the engine coolant.

The second chamber 606 accommodates the tube bundle 602, so as to realize the heat exchanger in which the exhaust gas heats the lubri-cating oil.

The internal combustion engine 1 is further equipped with an engine control unit (ECU) 7, which is connected to the valve 53, to the valve 54 and to the valve 62, so as to control their operations.

In particular, the ECU 7 is configured for controlling the operation of the valve 53 and of the valve 62 according to a strategy, which is schematically represented by the flowchart shown in figure 3.

The control strategy generally provides for monitoring an actual val-ue V of a parameter correlated with the temperature of the internal combustion engine 1.

In the present example, this parameter is the temperature of the en-gine coolant.

Alternatively, the parameter could be the temperature of the exhaust gas or the temperature of the lubricating oil.

As long as the actual value V is below a first threshold value Thl of the coolant temperature, the strategy provides for comanding the valve 53 to route the exhaust gas coming form the exhaust manifold 3 into the bypass conduit 52, in order to not be cooled by in the coo-ler 51.

By way of example, the first threshold value Thi of the coolant tem-perature can be 70°C.

If the actual value V is even below a second threshold value Th2 of the coolant temperature, lower than the first threshold value Thl, the strategy further provides for closing the valve 62, in order to prevent the lubricating oil to flow trough the heat exchanger 6.

By way of example, the second threshold value Th2 of the coolant tern-perature can be 10°C.

In this way, as long as the internal combustion engine 1 is very cold, typically at the very start of the engine, the exhaust gas is not cooled neither by the engine coolant nor by the lubricating oil, thereby preventing any overcool of the exhaust gas and quickening its warm-up.

In this condition, the lubricating oil is anyway slightly heated by the exhaust gas flowing in the heat exchanger 6, due to the heat con-duction between the exhaust gas and the amount of lubricating oil that is stationary inside the tube bundle 602.

When the actual value V of the coolant temperature exceeds the second threshold value Th2, the strategy provides for opening the valve 62, so as to allow the lubricating oil to effectively flow through the heat exchanger 6.

The valve 62 is kept open as long as the actual value v is comprised between the second threshold value Th2 and the first threshold value Thi.

In this way, the heat exchange between the lubricating oil and the exhaust gas is increased, due the continuous circulation of the lu-bricating oil.

As a consequence, the exhaust gas heats the lubricating oil, so as to quicken the warm-up of the latter, thereby reducing the engine fric-tions and the fuel consumption.

In this condition, the exhaust gas is not overcooled by the lubricat-ing oil, since the specific heat of the lubricating oil is about half of the specific heat of the engine coolant.

In order to better regulate the quantity of heat exchanged between the exhaust gas and the lubricating oil, while the actual value V of the coolant temperature is comprised between the first threshold val-ue Thi and the second threshold value Th2, the strategy can further provide for modulating the flow rate of lubricating oil flowing through the heat exchanger 6, provided that the valve 62 is a flow rate control valve.

When the actual value V of the coolant temperature exceeds the first threshold value Thi, the strategy provides for commanding the valve 53 so as to route the exhaust gas coming from the exhaust manifold 3 into the cooler 51, in order to be cooled by the engine coolant.

The valve 53 is kept in this configuration as long as the actual val-ue V is equal or greater than the first threshold value Thi.

In this way, when the internal combustion engine 1 reaches a normal operating temperature, the exhaust gas is properly cooled so as to effectively reduce the quantity of nitrogen oxides (NOt) which is pro- duced by the combustion processes inside the internal combustion en-gine 1.

In this condition, the valve 62 can be kept closed or can be opened indifferently.

The strategy can be managed with the help of a computer program com-prising a program-code for carrying out all the steps described above.

The computer program is stored in a data carrier 8 associated to the ECU 7.

In this way, when the ECU 7 executes the computer program, all the steps of the embodiments of the method described above are carried out.

While at least one exemplary embodiment has been presented in the foregoing summary 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 foregoing summary 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 embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. D4S

Claims (13)

1. Internal combustion engine (1) equipped with an intake manifold (2), an exhaust manifold (3), a lubricating circuit (4) and an ex-haust gas recirculation system (5), the exhaust gas recirculation system (5) comprising a main conduit (50) that fluidly connects the exhaust manifold (3) with the intake manifold (2), a cooler (51) lo-cated in the main conduit (50), a bypass conduit (52) connected to the main conduit (50) so as to bypass the cooler (51), and a first valve (53) for alternatively routing the exhaust gas from the exhaust manifold (3) towards the cooler (51) or towards the bypass conduit (52), wherein an heat exchanger (6) is located in the bypass conduit (52) and is connected to the lubricating circuit (4).

2. Internal combustion engine (1) according to claim 1, wherein a second valve (62) is located in a conduit (60) connecting the heat exchanger (6) with the lubricating circuit (4).

3. Internal combustion engine (1) according to claim 2, wherein the second valve (62) is a flow rate control valve.

4. Internal combustion engine (1) according to claim 2, wherein the first valve (53) and the second valve (62) are connected to an engine control unit (7).

5. Internal combustion engine (1) according to claim 1, wherein the cooler and the heat exchanger have a corrmon external casing (603).

6. Method for operating an internal combustion engine (1) according to any of the preceding claims, comprising the steps of: -monitoring an actual value (V) of a parameter correlated with an engine temperature, -routing exhaust gas from the exhaust manifold (3) towards the heat exchanger (6), if the actual value (V) of the parameter is lower than a first threshold value (Thi) of the parameter, -routing the exhaust gas form the exhaust manifold (3) towards the cooler (51), if the actual value (V) of the parameter is equal or greater than the first threshold value (Thi) of the parameter.

7. Method according to claim 6, comprising the further steps of: -preventing lubricating oil to flow through the heat exchanger (6), if the actual value (V) of the parameter is lower than a second thre-shold value (Th2) of the parameter, -allowing lubricating oil to flow through the heat exchanger (6), if the actual value (V) of the parameter is equal or greater than the second threshold value (Th2) of the parameter, the second threshold value (Th2) being lower than the first threshold value (Thi).

8. Method according to claim 7, comprising the further step of mod- ulating the flow rate of lubricating oil flowing through the heat ex-changer (6), if the actual value (V) of the parameter is comprised between the first threshold value (Thi) and the second threshold val-ue (Th2).

9. Method according to claim 6, wherein the parameter is chosen from engine coolant temperature, lubricating oil temperature and exhaust gas temperature.

10. Computer program comprising a computer-code for carrying out a method according to any of the claims from 6 to 9.

11. Computer program product on which the computer program according to claim 10 is stored.

12. Control apparatus for an internal combustion engine (1), compriS-ing an ECU (7), a data carrier (8) associated to the ECU (7), and a computer program according to claim 10 stored in the data carrier (8).

13. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 10.