Charging system of an internal combustion engine

Abstract

A charging system 20 of an internal combustion engine comprises a compressor 22 to compress intake air 41 and produce a pressure that is higher than a boost pressure of the engine. The charging system

Description

Charging system of an internal combustion engine The present invention relates to a charging system of an internal combustion engine and a method for providing boost air to a cylinder of an internal combustion engine. To optimise the performance of modern internal combustion engines (combustion engines or internal combustion engines) in both purely combustion-powered vehicles and in hybrid vehicles comprising an internal combustion engine and an electric drive, the so-called turbocharger is well known in the prior art. It increases the density of the intake air for the cylinders and thus also the filling of the cylinder. The turbocharger is typically operated using the energy of the exhaust gas mass flow that is discharged during the exhaust stroke of the cylinders. The energy is extracted from the exhaust gas mass flow by a turbine and transmitted via a common shaft to the respective compressor for compressing the intake air. To further increase the density of the charge air (boost air) and with it also the power density of the internal combustion engine, a boost air cooler can be provided downstream of the compressor. The cooler charge air reduces the knocking tendency of gasoline engines, so that optimal ignition timing in terms of the centre of gravity of the combustion can be applied. This results in increased combustion efficiency and reduced fuel consumption. Such a system is disclosed in patent document US 2011 / 209473 A1, for example. Patent document DE 10 2019 006 517 A1 discloses an internal combustion engine with an exhaust gas turbocharger comprising a turbine, a compressor and an intercooler, wherein a further turbine which drives a generator is provided downstream of the intercooler as well. Patent document DE 10 2011 018 570 A1 discloses an engine to which compressed air is supplied during operation by means of a compressor. The compressor is driven as a turbocharger by exhaust gas being discharged from the internal combustion engine, wherein more air is provided via the compressor than is required by the engine. The excess air is expanded via a turbine which drives a generator and fed back in upstream of the compressor. Patent specification DE 10 2010 035 085 B4 furthermore discloses a motor vehicle with an internal combustion engine comprising an exhaust gas turbocharger, wherein a turbine, which can be driven by the air compressed by the compressor and is coupled to an electrical generator, is disposed in the intake tract downstream of the compressor. An intercooler is disposed downstream of the compressor and the turbine. In view of the described prior art, the invention seeks to provide a charging system for an internal combustion engine that further increases the power density of an internal combustion engine and at the same time enables a compact design of the system. The present invention also seeks to provide a corresponding method for providing boost air to a cylinder of an internal combustion engine. Aspects of the invention are as claimed in the independent claims. Advantageous further developments of the invention are contained in the dependent claims. It should be noted at this point that the configurations of the invention disclosed in the description as advantageous embodiments of the apparatus according to the invention are correspondingly likewise disclosed as advantageous embodiments of the method according to the invention. The charging system according to an aspect of the invention comprises a compressor, which is configured to compress intake air and produce a pressure that is higher than a boost pressure of the internal combustion engine. The boost pressure is understood to be the pressure of the intake air that said intake air has for filling the cylinders. Therefore, when the cylinder is being filled, the intake air is compressed to a pressure level that is higher than that of the boost air of the internal combustion engine. The charging system further comprises a first energy recovery turbine which is configured to recover energy from an exhaust gas mass flow discharged from a cylinder, wherein the compressor and the first energy recovery turbine are disposed together on a first shaft and the recovered energy is thus transmitted directly to the compressor. The charging system according to an aspect of the invention also comprises a cooling turbine which is configured to expand, and thus also cool, the (intake) air compressed by the compressor to the boost pressure required by the cylinder. A second energy recovery turbine is provided as well, which, like the first energy recovery turbine, is configured to recover energy from an exhaust gas mass flow discharged from the cylinder, wherein the first and the second energy recovery turbine are preferably disposed in parallel and the exhaust gas mass flow therefore separates in order to operate the two energy recovery turbines. The second energy recovery turbine and the cooling turbine are disposed on a common second shaft. According to the invention, the second shaft is coupled to at least one energy sink. In the context of this application, an energy sink is intended to be understood as either an energy consumer or an energy store that can receive and consume or store the rotational energy of the shaft. Coupling is thus intended to be understood to be a connection that allows the energy of the shaft to be transmitted. An energy converter, which converts the rotational energy of the second shaft into electrical energy, for example, in order to make it usable, is preferably provided as well. In comparison to the prior art, the charging system according to aspects of the invention enables additional cooling of the boost air and thus a further increase in the power density of the internal combustion engine, wherein the additional energy used for this purpose can largely be made usable again. At the same time, the charging system with the two shafts enables a compact and efficient arrangement. In an advantageous embodiment of the invention, the charging system further comprises a boost air cooler which is configured to cool the air compressed by the compressor in addition to the cooling turbine. This boost air cooler is preferably disposed between the compressor and the cooling turbine. The boost air cooler provides an efficient way to further cool the boost air. The boost air cooler can furthermore be operated by the energy produced at the second shaft. In a further advantageous embodiment of the invention, the cooling turbine is configured to expand and cool the compressed air such that the temperature of the compressed air is the same as or preferably less than an ambient temperature of the intake air when it is drawn in upstream of the compressor. This makes it possible to further increase the power density. The second shaft is moreover preferably coupled directly to the drive train, in particular the gear drive of the internal combustion engine, as an energy sink. Alternatively or additionally, the coupling between the second shaft and energy sink is effected mechanically, in particular by means of a planetary gear. The mechanical coupling, in particular by means of a planetary gear, is a compact, inexpensive and long lasting way to transmit power. In a preferred embodiment of the invention, the coupling of the second shaft to the energy sink takes place between the cooling turbine and the second energy recovery turbine. Thus, in embodiments with a planetary gear as a coupling, said planetary gear is located on the second shaft between the cooling turbine and the second energy recovery turbine. Arranging the coupling in this manner makes it possible to reduce the effort involved in mounting the second shaft and minimise the length of the shaft. Alternatively, embodiments of the invention are also conceivable, in which the coupling of the second shaft to the energy sink is disposed outside the cooling turbine and the second energy recovery turbine, in particular on the side of the cooling turbine. Further preferred is an embodiment of the invention comprising an air filter which filters the intake air prior to the compression stage in the compressor. This makes it possible to ensure that no harmful impurities enter the compressor and the cooling stages or even the cylinder. The method according to an aspect of the invention for providing boost air for a cylinder of an internal combustion engine first comprises the step of compressing the intake air, in which the air to be compressed is compressed by a compressor to a pressure that is higher than a boost pressure of the internal combustion engine. The compressed air is then expanded to the boost pressure and cooled by at least a cooling turbine. The compressed air is preferably cooled by a boost air cooler, in particular prior to being cooled by the cooling turbine, and only then enters the cooling turbine. Energy is furthermore recovered from the exhaust gas mass flow by means of a first and a second energy recovery turbine, wherein the energy recovered by the first energy recovery turbine is used to operate the compressor. According to aspects of the invention, the second energy recovery turbine and the cooling turbine moreover transmit energy to a second shaft and the energy of the second shaft, which is then present as rotational energy, is transmitted to an energy sink. An embodiment and advantageous aspects of the invention will be explained in more detail in the following with reference to the accompanying drawing. Fig. 1 shows an embodiment of the charging system 20 according to an embodiment of the invention for an internal combustion engine 10 Fig. 1 shows an embodiment of the charging system 20 according to an embodiment of the invention for an internal combustion engine 10. It comprises an engine block 11 and six cylinders 12. The charging system 20 is responsible for supplying the boost air 44 required for combustion in the cylinders 12. The components of the charging system 20 are a compressor 22, an intercooler 23, a cooling turbine 24 and a first and a second energy recovery turbine 25, 26. The intake air 41 drawn in by the internal combustion engine 10 first reaches the air filter 21, which first filters the intake air 41 and thus removes pollutants or constituents that are harmful to the components of the charging system 20 from the air. The intake air 41 then enters a compressor 22, which compresses the intake air 41 to a pressure that is higher than the boost pressure of the boost air when it flows into the cylinder 12. Compression also increases the temperature of the compressed air 42. To lower the temperature again, the compressed air 42 is directed into the boost air cooler 23, from where the cooled air 43 passes to the cooling turbine 24. There it is expanded to the boost pressure, which also cools it. This arrangement makes it possible to cool the boost air 44 to such an extent that its temperature is below the temperature of the intake air 41 and thus also below the ambient temperature and the necessary boost pressure is nonetheless present. The cooled boost air 44 then enters the cylinders 12. After combustion in the cylinders 12, an exhaust gas mass flow 45 is discharged during the exhaust stroke of the cylinder, is divided and enters the first and the second energy recovery turbines 25, 26. The two energy recovery turbines are thus disposed in parallel. The first energy recovery turbine 25 is disposed with the compressor 22 on a common first shaft 31, wherein the first energy recovery turbine 25 can then operate the compressor 22. The second energy recovery turbine 26 is disposed with the cooling turbine 24 on a common second shaft 32. Thus both the second energy recovery turbine 26 and the cooling turbine 24 transmit an accelerating torque to the second shaft 32. This is coupled to an energy sink via a gearing 33, so that the rotational energy transmitted to the second shaft 32 can either be directly reused, for example to operate the boost air cooler 23, or temporarily stored in a battery or other energy store. The gearing 33 is embodied as a planetary gear, for example, and in the shown embodiment is disposed in the vicinity of the cooling turbine 24 on a portion of the second shaft 32 that is not located between the cooling turbine 24 and the second energy recovery turbine 26. The shown embodiment makes it possible to provide a charging system 20 which combines a compact design with efficient cooling of the boost air pressure and makes the best possible use of the expended energy. The arrangement of the first and the second energy recovery turbines 25, 26 enables optimal recovery of the energy contained in the exhaust gas mass flow 45. Even in the event that a maximum boost pressure is exceeded by the compression, the boost air 44 can be expanded again by the cooling turbine 24 and thus cooled, wherein greater expansion results in greater cooling. The exhaust gas mass flow can alternatively be directed more to the second energy recovery turbine 26, so that the compressor is driven to a lesser extent by the first energy recovery turbine 25. Supplying the second energy recovery turbine 26 with a larger exhaust gas mass flow causes a larger proportion of its energy to be transmitted to the second shaft 32 and passed from there via the coupling to an energy sink where it can be further used. The energy of the exhaust gas mass flow can thus always be recovered in the best possible way, even if the compressor is already compressing the intake air to a maximum pressure level. LIST OF REFERENCE SIGNS 10 Internal combustion engine 11 Engine block 12 Cylinder 20 Charging system 21 Air filter 22 Compressor 23 Boost air cooler 24 Cooling turbine 25 First energy recovery turbine 26 Second energy recovery turbine 31 First shaft 32 Second shaft 33 Gearing 41 Intake air 42 Compressed air 43 Cooled air 44 Boost air 45 Exhaust gas mass flow

Claims

Claims 1. Charging system for an internal combustion engine having at least one cylinder, comprising a compressor, which is configured to compress intake air and produce a pressure that is higher than a boost pressure of a boost air when the cylinder is being filled, a first energy recovery turbine which is configured to recover energy from an exhaust gas mass flow discharged from the cylinder, wherein the compressor and the first energy recovery turbine are disposed on a first shaft, a cooling turbine which is configured to expand and cool the compressed air to the required boost pressure, and a second energy recovery turbine which is configured to recover energy from an exhaust gas mass flow discharged from the cylinder, wherein the cooling turbine and the second energy recovery turbine are disposed on a second shaft, wherein the second shaft is coupled to at least one energy sink.

2. Charging system according to the preceding claim, wherein the charging system further comprises a boost air cooler which is configured to cool the air compressed by the compressor in addition to the cooling turbine.

3. Charging system according to any one of the preceding claims, wherein the boost air cooler is disposed between the compressor and the cooling turbine.

4. Charging system according to any one of the preceding claims, wherein the cooling turbine is configured to expand and cool the compressed air such that the temperature of the compressed air is the same as or preferably less than an ambient temperature of the intake air.

5. Charging system according to any one of the preceding claims, wherein the second shaft is coupled to the drive train as an energy sink.

6. Charging system according to any one of the preceding claims, wherein the coupling between the second shaft and the energy sink is effected by means of a planetary gear. / . Charging system according to any one of the preceding claims, wherein the coupling between the second shaft and the energy sink takes place between the cooling turbine and the second energy recovery turbine.

8. Charging system according to any one of the preceding Claims 1 to 6, wherein the coupling between the second shaft and the energy sink on the side of the cooling turbine takes place outside a portion on the second shaft between the cooling turbine and the second energy recovery turbine.

9. Charging system according to any one of the preceding claims, wherein the system further comprises an air filter which is configured to filter the intake air.

10. Method for providing boost air for a cylinder of an internal combustion engine, comprising the following steps: compressing intake air to compressed air by means of a compressor to a pressure that is higher than a boost pressure of the internal combustion engine, cooling the compressed air by means of a cooling turbine, wherein the compressed air is relaxed to the boost pressure and a resulting boost air is fed to the cylinder, recovering energy from the exhaust gas mass flow by means of a first energy recovery turbine and a second energy recovery turbine, wherein the recovered energy from the first energy recovery turbine (25) is used to operate the compressor, wherein the second energy recovery turbine and the cooling turbine transmit energy to a second shaft and the energy from the second shaft is transmitted to an energy sink.

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