EP2171245A1

EP2171245A1 - Apparatus for cooling recirculated exhaust gas of an internal combustion engine

Info

Publication number: EP2171245A1
Application number: EP08784703A
Authority: EP
Inventors: Eberhard Pantow; Georg Feldhaus; Simon Edwards
Original assignee: Behr GmbH and Co KG
Current assignee: Mahle Behr GmbH and Co KG
Priority date: 2007-07-26
Filing date: 2008-07-11
Publication date: 2010-04-07
Also published as: DE102007035443A1; WO2009012897A1

Abstract

The invention relates to an apparatus for cooling recirculated exhaust gas of an internal combustion engine (1), comprising a first heat exchanger (14) for cooling the exhaust gas, through which heat exchanger (14) the recirculated exhaust gas can flow, and at least one second heat exchanger (15) for cooling the exhaust gas, through which heat exchanger (15) the recirculated exhaust gas flows, wherein the second heat exchanger (15) is arranged downstream of the first heat exchanger, wherein a regulating element (16) is provided, by means of which a cooling performance of at least the second heat exchanger (15) can be regulated in an adjustable way, which cooling performance acts on the exhaust-gas flow.

Description

Device for cooling recirculated exhaust gas of an internal combustion engine

The invention relates to a device for cooling recirculated exhaust gas of an internal combustion engine according to the preamble of claim 1 and a motor vehicle with a device according to the invention.

EP 1 091 113 B1 describes an exhaust gas recirculation system for a diesel engine, in which, in a variant according to FIG. 2, a first exhaust gas cooler and a second exhaust gas cooler following it are provided. The first radiator is connected to the cooling circuit of the engine and the second radiator to a low-temperature cooling circuit of the engine.

It is the object of the invention to provide a device for cooling recirculated exhaust gas of an internal combustion engine, in which by simple means a power control of the exhaust gas cooling is achieved for adaptation to different operating ranges of the internal combustion engine.

This object is achieved according erfindungsge- measure for a device mentioned above with the characterizing features of claim 1. Due to the possibility of power control of at least the second heat exchanger may have special requirements for the temperature of the engine supplied exhaust gas can be met. These may depend primarily on the operating condition of the engine and here in particular on the applied load. The invention is not limited to two successively arranged heat exchangers, but also includes arrangements of more than two heat exchangers, wherein more than one of the heat exchangers may be regulated in its performance.

In an advantageous embodiment of the internal combustion engine is designed as a gasoline engine, in particular as gasoline engine with a direct fuel injection and / or a variable valve train. In such a gasoline engine exhaust gas recirculation can be useful not only to reduce pollutant emissions, especially nitrogen oxides (NOx), but also to optimize fuel consumption and thus reduce carbon dioxide. This raises the particular problem that the largest possible cooling of the recirculated exhaust gas is desired only at high or full load. In this case, a reduction in the combustion temperature is desired in order to be able to choose the ignition point more favorably due to the resulting lower tendency to knock. At very high loads, the function of temperature protection, which makes it possible to dispense in many areas with a consumption-intensive enrichment of the mixture, is added. Since the highest temperatures occur in the full load range in conjunction with the highest mass flows, the exhaust gas cooling must have a high maximum performance.

In the lower load range or at partial load, the exhaust gas recirculation is used in particular in the charged gasoline engine (suction at partial load) in the main of a Entdrosselung the engine. The cooling of the recirculated exhaust gas should prevent sufficient knocking only. A cooling beyond this would again lead to a stronger throttling and / or a deterioration of the mixture preparation. Another disadvantage of excessive exhaust gas cooling in the partial load range can be attributed to consist of the condensate. Overall, the device according to the invention is thus particularly advantageous in the exhaust gas recirculation, in particular in the case of turbocharged gasoline engines, since it allows a high maximum cooling capacity for the full load range with adjustable low cooling capacity in the partial load range to optimize fuel consumption.

In the interest of a cost-effective simplification of the device, the first heat exchanger is not adjustable adjustable in its cooling capacity. This also has the advantage that a minimum cooling capacity is reliably available due to the simple design of the first heat exchanger and can not be adversely affected by a malfunction of a control element.

In a first preferred embodiment of the invention, the control element comprises an exhaust valve for controlling the exhaust gas flow. Advantageously, a controllable by the control element bypass channel for at least partially bypassing the second heat exchanger is provided. As a result, the cooling of the exhaust gas flow can be changed particularly quickly and in a wide range by partially or completely diverting to the bypass duct. In a space-and cost-optimized detail design, the control element can be designed so that by means of the control element both a guide of the exhaust gas flow through the bypass channel is adjustable and the entire size of the recirculated exhaust gas flow.

In an alternative or supplementary embodiment, the control member comprises a coolant valve for adjustably controlling a coolant flow of the second heat exchanger. A cooling capacity control by influencing the coolant flow allows, inter alia, a particularly compact design of the heat exchanger and is structurally particularly simple and reliable realized. In a simple manner, the control member may comprise a thermostatic valve, with particular preference the thermostatic valve has an adjustable control behavior, in particular by means of an electrical heating element. Such controllable in their control characteristics thermostatic valves are also referred to as map thermostats. In a detailed design of the second heat exchanger in a partial load operation of the internal combustion engine is not substantially flowed through by a coolant, so that there is a reduced cooling capacity of the entire system especially in partial load operation. A negligible for the heat exchange residual flow may well be provided to obtain a constant information about the temperature in the second heat exchanger and to allow a rapid response of the thermostat to an increasing heat input through the exhaust gas.

Generally advantageously, at least one of the heat exchangers can be connected to a main cooling circuit of the internal combustion engine, whereby a flowing coolant for indirect exhaust gas cooling is provided in a simple manner. In a particularly simple and at the same time effective design, both the first and the second heat exchanger are connected to a main cooling circuit of the internal combustion engine.

Alternatively or additionally, at least one of the heat exchangers, in particular the second heat exchanger, can also be connected to a low-temperature coolant circuit. Such a low temperature circuit allows the cooling of the recirculated exhaust gas to temperatures well below the typical temperature of the engine cooling circuit. In this case, a separate air-circulated cooler of the low-temperature cooling circuit is regularly provided.

In an advantageous detailed embodiment of the invention, the first heat exchanger with respect to exhaust gas flow and coolant flow is operated in DC. As a result, lower wall temperatures occur in the inlet region of the exhaust gas. temperatures, which reduces the risk of local boiling of the coolant.

Further preferably, the second heat exchanger is operated countercurrently with respect to the exhaust gas flow and the coolant flow. Since the exhaust gas flow is already pre-cooled when entering the second heat exchanger and no longer has extreme temperatures, there is hardly any risk of boiling of the coolant in the second heat exchanger, so that the effective variant of countercurrent cooling is available for the second heat exchanger.

The device according to the invention can be used particularly advantageously with an internal combustion engine, which has a fresh gas charge, in particular an exhaust gas turbocharger, due to the aforementioned problem. In an advantageous development of the invention, a charge air cooler of the fresh gas charge and at least the second heat exchanger can have a common coolant circuit, in particular a low-temperature coolant circuit.

In the interest of minimizing components and making optimal use of space, it is generally advantageous for the first heat exchanger and the second heat exchanger to be designed as an integrated structural unit.

The invention also includes a motor vehicle, in particular passenger cars, with a device according to one of claims 1 to 18. Gasoline engines are widely used in passenger cars, with increasing demands on pollutant emissions and consumption optimization are made. Further advantages and features of the invention will become apparent from the embodiments described below and from the dependent claims.

Hereinafter, several preferred embodiments of the invention will be described and explained in more detail with reference to the accompanying drawings.

Fig. 1 shows a schematic representation of the cooling system of an internal combustion engine with exhaust gas recirculation according to the prior art.

Fig. 2 shows a schematic representation of an inventive

Contraption.

3 shows a first embodiment of the device according to the invention from FIG. 2. FIG. 4 shows a second embodiment of the device according to the invention from FIG. 2.

5 shows a third embodiment of the device according to the invention from FIG. 2.

6 shows the diagram of a control characteristic of the control element of the device from FIG. 5.

In Fig. 1, a known from the prior art arrangement of a trained as a gasoline engine 1 internal combustion engine with exhaust gas recirculation is shown. The internal combustion engine 1 has a mixture inlet on the inlet side with a throttle valve 2 and on the outlet side an exhaust pipe with a branch 4 arranged upstream of an exhaust gas turbocharger 3. The exhaust gas stream branched off at the branch 4 flows through an indirectly cooled exhaust gas cooler 5 and is adjustable in size via an adjustable exhaust valve 6. On the intake side, a charge air cooler 13 is provided between the exhaust gas turbocharger and the throttle valve in a known manner, which is designed here as a direct, air-flow-cooled heat exchanger. By the term indirect cooling is meant here that the exhaust gas cooler 5 is flowed through by a liquid coolant. This is connected via branches 7, 8 with a main cooling circuit of the internal combustion engine 1 connected. The main cooling circuit comprises a water pump 9, a coolant radiator 10 with fan 10a and an engine bypass 11, which is connected via a thermostat 12 for shortening a warm-up phase of the engine.

With regard to the arrangement of the exhaust gas cooler 5, which is parallel to the engine 1, the representation according to FIG. 1 can only be understood schematically. Additional means for controlling the coolant branches may be provided, such as a second water pump in the exhaust gas cooler branch, fixed throttle or adjustable throttle valves.

The embodiment according to the invention schematically illustrated in FIG. 2 comprises - with otherwise identical configuration of the internal combustion engine 1 - instead of the individual exhaust gas cooler 5 of FIG. 1 an arrangement of several heat exchangers, wherein a first heat exchanger 14 and downstream of the exhaust gas flow, a second heat exchanger 15 in series arranged one after the other.

Each of the two heat exchangers 14, 15 is designed as an indirect exhaust gas cooler and has ports 14a, 14b and 15a, 15b for the respective supply and discharge of a liquid coolant. In the embodiments shown, both heat exchangers 14, 15 are connected to the main cooling circuit of the engine 1. Depending on the requirements, the connection can be made separately for each cooler or by means of branches.

In order to prevent local boiling or overheating of the liquid coolant in the first heat exchanger 14 as possible, the first heat exchanger operated in DC. As a result, the incoming, particularly hot exhaust gas hits the entering, particularly cold coolant. On the outlet side, the coolant has its highest temperature, but only meets partially cooled exhaust gas, so that the risk of local overheating is low.

Depending on the requirements, the second heat exchanger 15 can be operated in direct current, so that incoming coolant encounters escaping exhaust gas, or else in countercurrent (see directional arrows at the connections 14a, 14b, 15a, 15b).

In Fig. 2 is schematically indicated that the first heat exchanger 14 is not adjustable in its cooling capacity and thus constantly provides its maximum power. Although this can fluctuate, for example during a warm-up phase of the engine 1, it does not represent a specifically controllable variable.

In contrast, the subsequent second heat exchanger 15 in its cooling capacity by means of a control member 16 (shown in Fig. 2 only schematically) adjustable variable. This can be reacted to various operating conditions of the engine, such as partial load or full load operation.

At partial load, supercharged gasoline engines are usually in the suction mode, so that a de-throttling of the engine is carried out by a recirculated exhaust gas flow. The temperature of the recirculated exhaust gas should not be so low that the effect of Entdrosselung is counteracted or even condensation occurs in the exhaust gas. Rather, the temperature should just be so low that knocking is avoided and there is sufficient freedom to set the ignition timing.

At full load, however, a maximum cooling of the recirculated exhaust gas is desired, so that the second heat exchanger 15 should usually provide its maximum cooling capacity in this operating range. FIG. 3 shows a first concrete exemplary embodiment of the device shown only schematically in FIG. 2. In this case, the second heat exchanger 15 comprises a bypass channel 15a, via which the exhaust gas stream can flow selectably selectable. The control member 16 is designed as an exhaust valve, in the present case in the form of a 3-way valve, and arranged in front of the second heat exchanger 15 and the bypass channel parallel thereto. The control member 16 is arranged downstream of the first heat exchanger, so that the input side, the entire cooled in the first heat exchanger exhaust gas stream enters the control member 16.

The partial flow of the exhaust gas conducted via the regulating member 16 onto the bypass 15a is not or only insignificantly cooled. The higher the proportion of the bypass gas flow, the smaller the cooling capacity that the second heat exchanger exerts on the recirculated exhaust gas flow.

The total size of the recirculated exhaust gas flow may also be adjustable via the 3-way valve, for example by adjustable alteration of the minimum cross section of the supply line from the first heat exchanger 14 to the second heat exchanger 15.

The embodiment shown in Fig. 4 is a modification of the embodiment of Fig. 3. The control member 16 for controlling the cooling capacity of the second heat exchanger 15 is also an exhaust valve. In the present case, the exhaust gas valve 16 is structurally designed such that the total amount of recirculated exhaust gas and the guidance of the exhaust gas can be adjusted either via the second heat exchanger or the bypass channel by means of a single valve spool 17. In the arrangement shown, this is done by the valve spool 17, depending on the deflection from a central position a more or less large cross section of a coming out of the first heat exchanger supply line 18 releases, whereby the total current regulated becomes. In the middle position of the valve spool 17 closes the supply line 18. A deflection to one side (deflection as shown in Fig. 4 to the left) passes the so-passed exhaust gas flow through the bypass passage and a deflection from the center position to the other side directs the exhaust gas to Cooling by the second heat exchanger 15. It is understood that depending on detail design, other flow paths of such a structurally optimized exhaust valve are possible.

Furthermore, in the exemplary embodiment according to FIG. 4, the bypass channel 15 a is integrated with the heat exchanger 15. Such integrated types of bypass duct and exhaust gas heat exchanger are known from the prior art.

As schematically indicated in FIG. 4, the first heat exchanger 14 and the second heat exchanger 15 can form an integrated structural unit, wherein in the present example the control member 16 forms a connecting element between the heat exchangers 14, 15 by means of a housing-like outer wall 19.

Another embodiment of the invention is shown in FIG. Here, the Regelied 16 is designed to adjust the cooling capacity of the second heat exchanger as an output side, so arranged in the return coolant valve of the second heat exchanger. Depending on the thus adjustable coolant flow through the second heat exchanger thus a variable cooling capacity for the exhaust gas flow is adjusted.

The control member 16 is designed as a fast map thermostat. A map thermostat comprises an electric heater, by means of which the control characteristics can be influenced to a certain extent depending on the requirements. At low loads of the engine, the second heat exchanger 15 is not or only slightly flowed through by coolant and at high loads, the flow of coolant through the thermostat 16 is released. The thermostat also allows a small leakage flow in the closed state to allow a quick opening and to obtain information about the load condition of the engine via the outlet-side coolant temperature. There is a monotone relationship between load and coolant temperature. As the beginning of the opening for the thermostat, a temperature is suitably selected, which is above the expected for the part-load operation coolant temperatures.

Typically, the main thermostat 12 of the engine cooling circuit regulates the coolant temperature to a minimum of 85 ⁰ C. In map control up to 110 ⁰ C are allowed in partial load. From this, a temperature between about 90 ⁰ C and 115 ⁰ C. arises for the start of opening of the thermo- mostats 16 of the second heat exchanger 15 in order to ensure a good control, should the flow rate after start of opening approximately linearly increase with temperature. The maximum opening should be at a temperature that still allows a further increase in temperature through the heat exchanger 15.

In Fig. 6 of the thermostat 16 temperature-dependent controlled coolant flow V / t is plotted against the temperature T.

In a further alternative embodiment, which is likewise compliant with the illustrations in FIGS. 2 to 5, the second heat exchanger 15 is connected via its connections 15a, 15b to a separate low-temperature coolant circuit (not shown). Suitably, this low-temperature coolant circuit also cools an indirect intercooler. A radiator for dissipating the heat of the low-temperature coolant to the surroundings is arranged in front of the vehicle in front of the coolant radiator 10 (not shown). In a version with a coolant control As in Fig. 5 would be provided corresponding to the lower temperatures of Fig. 6 deviating control characteristics of the thermostat.

It goes without saying that the individual features of the various exemplary embodiments can be meaningfully combined with one another. Thus, it may be provided, for example, that a device according to the invention has both a power control via an exhaust valve and a bypass as well as a power control via a coolant valve.

Claims

Patent claims

1. A device for cooling recirculated exhaust gas of an internal combustion engine (1), comprising a first, by the recirculated exhaust gas flow-through heat exchanger (14) for cooling the exhaust gas, and at least a second, durchström- by the recirculated exhaust gas ble heat exchanger (15) for cooling the exhaust gas, wherein the second heat exchanger (15) is arranged downstream of the first heat exchanger, characterized in that a control member (16) is provided, by means of which an acting on the exhaust gas flow cooling capacity of at least the second heat exchanger (15) is adjustable adjustable.

2. Apparatus according to claim 1, characterized in that the internal combustion engine (1) is designed as a gasoline engine, in particular as gasoline engine with a direct fuel injection and / or a variable valve train.

3. Device according to claim 1, characterized in that the first heat exchanger (14) is not adjustable adjustable in its cooling capacity.

4. Device according to one of the preceding claims, characterized in that the regulating member (16) comprises an exhaust valve for controlling the exhaust gas flow.

5. Apparatus according to claim 4, characterized in that one of the control element (16) controllable bypass channel (15a) for at least partially bypassing the second heat exchanger (15) is provided.

6. Apparatus according to claim 5, characterized in that by means of the control element (16) both a guide of the exhaust gas flow through the bypass channel (15 a), and the entire size of the recirculated exhaust gas flow is adjustable.

7. Device according to one of the preceding claims, characterized in that the regulating member (16) comprises a coolant valve for adjustably controlling a coolant flow of the second heat exchanger (15).

8. The device according to claim 7, characterized in that the regulating member (16) comprises a thermostatic valve.

9. Apparatus according to claim 8, characterized in that the thermostatic valve (16) has an adjustable control behavior, in particular by means of an electric heating element.

10. Device according to one of claims 7 to 9, characterized in that the second heat exchanger (15) in a partial load operation of the internal combustion engine is not substantially flowed through by a coolant.

11. Device according to one of the preceding claims, characterized in that at least one of the heat exchangers (14, 15) is connected to a main cooling circuit of the internal combustion engine.

12. The apparatus of claim 1 1, characterized in that both the first and the second heat exchanger (14, 15) are connected to a main cooling circuit of the internal combustion engine.

13. Device according to one of claims 1 to 1 1, characterized in that at least one of the heat exchangers (14, 15), in particular the second heat exchanger (15), is connected to a low-temperature coolant circuit.

14. Device according to one of the preceding claims, character- ized in that the first heat exchanger (14) with respect to exhaust gas flow and coolant flow is operated in DC.

15. Device according to one of the preceding claims, characterized in that the second heat exchanger (15) with respect to exhaust gas Ström and coolant flow is operated in countercurrent.

16. Device according to one of the preceding claims, characterized in that the internal combustion engine (1) has a fresh gas charge, in particular an exhaust gas turbocharger (3).

17. The apparatus according to claim 16, characterized in that a charge air cooler of the fresh gas charge and at least the second heat exchanger (15) have a common coolant circuit, in particular a low-temperature coolant circuit.

18. Device according to one of the preceding claims, characterized in that the first heat exchanger (14) and the second heat exchanger (15) are formed as an integrated structural unit.

19. Motor vehicle, in particular passenger car, comprising a device according to one of claims 1 to 18.