Internal combustion engine having an exhaust heat recovery system as well as a method for recovering exhaust heat

Abstract

An internal combustion engine having at least one combustion chamber, the internal combustion engine being connected via the exhaust thereof with an exhaust system. Disposed in the exhaust system is a heat exchanger of an exhaust heat recovery system, which can be used to transfer the waste heat of the exhaust gas to an operating fluid of the exhaust heat recovery system. Furthermore, the internal combustion engine is couplable to an air-conditioning compressor of an air-conditioning circuit. The exhaust heat recovery system has a further heat exchanger, in which the waste heat of a compressed refrigerant of the air-conditioning circuit is transferred to the operating fluid of the exhaust heat recovery system. A method for recovering the exhaust heat from such an internal combustion engine, an operating fluid of the exhaust heat recovery system being heated in a first method step by the waste heat of a compressed refrigerant of the air-conditioning circuit and, in a second method step, by the waste heat of the exhaust gas from the internal combustion engine.

Claims

1. An exhaust system and an exhaust heat recovery system of an internal combustion engine comprising at least one combustion chamber, wherein the exhaust system comprises a first heat exchanger configured to transfer a waste heat of an exhaust gas from the internal combustion engine to an operating fluid of the exhaust heat recovery system, wherein the exhaust heat recovery system has a second heat exchanger, in which a waste heat of a compressed refrigerant of an air-conditioning circuit can be transferred to the operating fluid of the exhaust heat recovery system, and wherein the air-conditioning circuit has an air-conditioning compressor and a refrigerant condenser, the second heat exchanger being traversed by the flow of the refrigerant, which is compressed by the air-conditioning compressor, before the compressed refrigerant enters the refrigerant condenser.

2. The exhaust system and the exhaust heat recovery system as recited in claim 1, the exhaust heat recovery system further comprising a pump for the operating fluid, wherein the second heat exchanger is disposed in the operating fluid circuit downstream of the pump and upstream of the first heat exchanger, wherein the second heat exchanger is traversed by the flow of the exhaust gas from the internal combustion engine.

3. The exhaust system and the exhaust heat recovery system as recited in claim 1, wherein the exhaust heat recovery system further comprises an expansion engine in the operating fluid circuit, and the expansion engine is configured to drive a motor and/or a generator.

4. The exhaust system and the exhaust heat recovery system as recited in claim 3, wherein the expansion engine is couplable via a power split device optionally to the internal combustion engine and/or to an electric drive motor or generator.

5. The exhaust system and the exhaust heat recovery system as recited in claim 3, wherein the exhaust heat recovery system further comprises a pump for the operating fluid, and a condenser configured in the operating fluid circuit downstream of the expansion engine and upstream of the pump.

6. The exhaust system and the exhaust heat recovery system as recited in claim 5, wherein the condenser has a refrigerant inlet and a refrigerant return, which communicate with a cooling-water circuit of the internal combustion engine.

7. The exhaust system and the exhaust heat recovery system as recited in claim 5, wherein a reservoir for the operating fluid is configured downstream of the condenser and upstream of the pump.

8. The exhaust system and the exhaust heat recovery system as recited in claim 1, wherein the operating fluid of the exhaust heat recovery system is an alcohol.

9. The exhaust system and the exhaust heat recovery system as recited in claim 1, wherein, the air-conditioning circuit includes an expansion tank downstream of a refrigerant condenser and upstream of a refrigerant evaporator.

10. The exhaust system and the exhaust heat recovery system as recited in claim 1, wherein the refrigerant of the air-conditioning circuit is carbon dioxide.

11. A method for recovering exhaust heat from an internal combustion engine comprising at least one combustion chamber, wherein the internal combustion engine is connected to an exhaust system and an exhaust heat recovery system of the internal combustion engine, wherein the exhaust system comprises a first heat exchanger configured to transfer a waste heat of an exhaust gas from the internal combustion engine to an operating fluid of the exhaust heat recovery system, wherein the exhaust heat recovery system has a second heat exchanger, in which a waste heat of a compressed refrigerant of an air-conditioning circuit can be transferred to the operating fluid of the exhaust heat recovery system, wherein the air-conditioning circuit has an air-conditioning compressor and a refrigerant condenser, the second heat exchanger being traversed by the flow of the refrigerant, which is compressed by the air-conditioning compressor, before the compressed refrigerant enters the refrigerant condenser, the method comprising: heating an operating fluid of an exhaust heat recovery system by a waste heat of a compressed refrigerant of the air-conditioning circuit and heating the operating fluid by a waste heat of exhaust gas from the internal combustion engine.

12. The method as recited in claim 11, further comprising compressing the refrigerant to an operating pressure of at least 20 bar.

13. The method as recited in claim 11, further comprising transferring the waste heat of the compressed refrigerant downstream of a pump to the operating fluid of the exhaust heat recovery system.

14. The method as recited in claim 11, further comprising driving an air-conditioning compressor of the air-conditioning circuit by a traction means.

15. The method as recited in claim 11, further comprising compressing the refrigerant to an operating pressure of at least 100 bar.

16. The method as recited in claim 14, wherein the traction means includes a chain or a belt of a rotating shaft of the internal combustion engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will be explained in the following in exemplary embodiments with reference to the accompanying drawings. The same reference numerals in the various figures thereby denote identical components or components having the same function, where:

(2) FIG. 1 shows a preferred exemplary embodiment of an internal combustion engine having an exhaust system, an exhaust heat recovery system, as well as an air-conditioning circuit;

(3) FIG. 2 is a diagram of the pressure as a function of the enthalpy in the air-conditioning circuit in the case of an internal combustion engine according to the present invention; and

(4) FIG. 3 is a flow chart for implementing a method according to the present invention for recovering the exhaust-gas heat from an internal combustion engine.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows an internal combustion engine 10 having a combustion chamber 12, which is provided for driving a motor vehicle. In FIG. 1, internal combustion engine 10 is in the form of a six-cylinder in-line engine. Alternatively possible, however, are also other variants, preferably having 2-12 cylinders. Alternatively, internal combustion engine 10 may also be realized as a V engine or a boxer engine. Internal combustion engine 10 has a coolant circuit 18, via which the engine block of internal combustion engine 10 is cooled to dissipate the waste heat from internal combustion engine 10. Combustion engine 10 is coupled via exhaust 14 thereof to an exhaust system 20. Exhaust system 20 includes an exhaust duct 22, in which are disposed a turbine of an exhaust-gas turbocharger 16 in the direction of flow of an exhaust gas from internal combustion engine 10 through exhaust duct 22, and, downstream of the turbine of exhaust-gas turbocharger 16, a plurality of exhaust gas aftertreatment components 24, 26, as well as a heat exchanger 32 of an exhaust heat recovery system 30. A preferred specific embodiment of the present invention provides that internal combustion engine 10 be in the form of a compression-ignition diesel engine, and that exhaust gas aftertreatment components 24, 26 include an oxidation catalytic converter, an NOx storage catalytic converter, a particulate filter, and/or a catalytic converter for selectively catalytically reducing nitrogen oxides.

(6) Alternatively or additionally, the exhaust system, in particular in the case of an Otto engine, may also include a three-way catalytic converter or a four-way catalytic converter. Provided downstream of heat exchanger 32 is an exhaust-gas flap 28, which may be used to at least partially seal exhaust duct 22 in order to increase the exhaust gas back pressure. As exhaust heat recovery unit 84, exhaust gas aftertreatment components 24, 26 and heat exchanger 32 may also be configured in a shared housing 82 to simplify the installation of exhaust system 20. Exhaust-gas flap 28 may likewise be integrated in this exhaust heat recovery unit 84.

(7) In addition to heat exchanger 32, which also serves as an evaporator 32 for an operating fluid 39 of exhaust heat recovery system 30, exhaust heat recovery system 30 includes an expansion engine 34, a condenser 36, a pump 40, as well as a further heat exchanger 42 that is used to cool a compressed refrigerant 71 of an air-conditioning circuit 60. Exhaust heat recovery system 30 also includes a reservoir 38 for operating fluid 39, in particular an organic working medium, preferably alcohol or an alcohol-water mixture, especially ethanol or an ethanol-water mixture. Reservoir 38 is connected via a power line to pump 40, in which operating fluid 39 is compressed. The compressed working medium is fed to further heat exchanger 42 where it absorbs the waste heat of a pressurized refrigerant 71 and feeds it via a feed line 48 to heat exchanger 32. In heat exchanger 32, the waste heat of the exhaust-gas flow of internal combustion engine 10 is transferred to the operating fluid, and the operating fluid is converted into the gaseous state of aggregation. The thereby produced steam is fed via a steam line 44 to expansion engine 34, which is operatively connected to a hybrid module 50. By way of a power split device 58, expansion engine 34 may be connected optionally to internal combustion engine 10 via a mechanical drive shaft 56 or to a motor/generator 52 for generating electric current. Motor/generator 52 is connected to an electrical system 54 of a motor vehicle and is able to temporarily store the electrical energy in a battery 55.

(8) Disposed downstream of expansion engine 34 in exhaust heat recovery system 30 is a condenser 36, which has a refrigerant inlet 46 and a refrigerant return 47 and is connected to cooling-water circuit 18 of internal combustion engine 10. In condenser 36, the operating fluid of exhaust heat recovery system 30 is returned to the liquid state of aggregation before it is fed back to pump 40 via a return line 49.

(9) Internal combustion engine 10 is couplable via a traction means, in particular a chain or a belt, to an air-conditioning compressor 62 of air-conditioning circuit 60. Besides air-conditioning compressor 62, air-conditioning circuit 60 includes further heat exchanger 42, a refrigerant condenser 68, an expansion tank 70 and a refrigerant evaporator 76. Air-conditioning compressor 62 is connected via a line 64 to further heat exchanger 42, where refrigerant 71, which is compressed by air-conditioning compressor 62, transfers the heat thereof to operating fluid 39 of exhaust heat recovery system 30. Further heat exchanger 42 is connected via another line 66 to a refrigerant condenser 68 of air-conditioning circuit 60. Provided downstream of refrigerant condenser 68 is an expansion tank 70 in which refrigerant 71 is stored. Provided downstream of expansion tank 70 is a high pressure valve 72. High pressure valve 72 is connected via a line 74 to a refrigerant evaporator 76 in which refrigerant 71 is expanded and evaporated, energy being extracted therefrom, causing it to cool considerably. This cold is utilized for air conditioning a passenger compartment of a motor vehicle. Furthermore, a valve 78 and an evaporation volume 80 are provided in the air-conditioning circuit, in order to collect the expanded refrigerant again and feed it to air-conditioning compressor 62.

(10) Air-conditioning compressor 62 compresses refrigerant 71 to a pressure of at least 20 bar, preferably at least 100 bar, refrigerant 71, in particular carbon dioxide, heating up considerably. This heat is transferred via further heat exchanger 42 to operating fluid 39 of exhaust heat recovery system 30, the compressed refrigerant being cooled at the same time.

(11) Internal combustion engine 10 is operatively connected to a control unit 90, via which air-conditioning circuit 60 as well as exhaust heat recovery system 30 are controlled.

(12) FIG. 2 shows a pressure-enthalpy diagram that illustrates the processes in air-conditioning circuit 60.

(13) FIG. 3 shows a flow chart for implementing a method according to the present invention for recovering exhaust heat. In a first method step <100>, air-conditioning compressor 62 is operated, and refrigerant 71 is compressed. In a method step <110>, compressed refrigerant 71 is fed to further heat exchanger 42. In a method step <120>, compressed refrigerant 71 is cooled by operating fluid 39 of exhaust heat recovery system 30 and subsequently fed to refrigerant condenser 68. Refrigerant 71 is expanded in a method step <130> and evaporated in refrigerant evaporator 76 in a method step <140>. Refrigerant 71 thereby cools and transfers this cold to an air flow that is fed to the passenger compartment of the motor vehicle. In a method step <150>, the expanded refrigerant is collected again and fed to air-conditioning compressor 62.

(14) In a method step <200>, operating fluid 39 of exhaust heat recovery system 30 is delivered from reservoir 38 into further heat exchanger 42. There, in a method step <210>, hot, compressed refrigerant 71 transfers the heat thereof to colder operating fluid 39, so that energy is fed to exhaust heat recovery system 30 and extracted from air-conditioning circuit 60. Method steps <120> and <210> are thereby always executed simultaneously. Heated operating fluid 39 is fed to heat exchanger 32, where it is heated further by the exhaust-gas flow and evaporates in a method step <220>. Vapor-state operating fluid 39 is fed via steam line 44 to expansion engine 34 and drives it in a method step <230>. After flowing through expansion engine 34, operating fluid 39 is fed to condenser 36, it being cooled in a method step <240> and converted again from the gaseous state of aggregation into the liquid state of aggregation. In a method step <250>, the cooled operating fluid is collected and fed to pump 40 again, whereby the circuit of the exhaust heat recovery system closes.

(15) By additionally transferring the waste heat of compressed refrigerant 71 to operating fluid 39 of exhaust heat recovery system 30, the efficiency of internal combustion engine 10 may be enhanced since the dissipated heat may be utilized, and less energy needs to be provided to drive the air-conditioning compressor by combusting fuel.

LIST OF REFERENCE NUMERALS

(16) 10 internal combustion engine 12 combustion chamber 14 exhaust 16 exhaust-gas turbocharger 18 turbine 20 exhaust system 22 exhaust duct 24 first exhaust gas aftertreatment component 26 second exhaust gas aftertreatment component 28 exhaust-gas flap 30 exhaust heat recovery system 32 heat exchanger/evaporator 34 expansion engine 36 condenser 38 reservoir 39 operating fluid WHR (waste heat recovery) system 40 pump 42 heat exchanger/air-conditioning condenser 44 steam line 46 refrigerant inlet 47 refrigerant return 48 feed line 49 return line 50 hybrid module 52 motor/generator 54 vehicle electrical system 55 battery 56 mechanical drive 58 power split device 60 air-conditioning circuit 62 air-conditioning compressor 64 line 66 further line 68 refrigerant condenser 70 expansion tank 71 refrigerant 72 high pressure valve 74 line 76 refrigerant evaporator 78 valve 80 evaporation 82 housing 84 exhaust gas aftertreatment unit 90 control unit