Supercharging Device for an Internal Combustion Engine of a Motor Vehicle, and Method for Operating a Supercharging Device of This Kind

Abstract

A supercharging device for an internal combustion engine of a motor vehicle includes: an exhaust-gas turbocharger having a turbine wheel that can be driven by exhaust gas from the internal combustion engine and a first compressor wheel that can be driven by the turbine wheel, by which first compressor wheel air being supplied to the internal combustion engine is compressed; an electric compressor having an electric machine and a second compressor wheel that can be driven by the electric machine, by which second compressor wheel air being supplied to the internal combustion engine is compressed; and an overrun air recirculation device associated with the first compressor wheel, by which, when there is a reduction in load on the internal combustion engine, a portion of the air compressed by the first compressor wheel can be branched off at a first point arranged downstream of the first compressor wheel and can be fed back from the first point to a second point arranged upstream of the first compressor wheel, wherein the supercharging device supplies the second compressor wheel with the branched-off air such that the second compressor wheel and, via the second compressor wheel, the electric machine, can be driven by the branched-off air.

Claims

1. A supercharging device for an internal combustion engine of a motor vehicle, comprising: at least one exhaust-gas turbocharger having a turbine wheel which is drivable by exhaust gas of the internal combustion engine and a first compressor wheel which is drivable by the turbine wheel and which is provided for compressing air for feeding to the internal combustion engine; at least one electric compressor having an electric machine and a second compressor wheel which is drivable by the electric machine and which is provided for compressing air for feeding to the internal combustion engine; and an overrun air recirculation device assigned to the first compressor wheel and by which, in an event of a load reduction of the internal combustion engine, at least a part of the air compressed by the first compressor wheel is branched off at a first point arranged downstream of the first compressor wheel and is returned from the first point to a second point arranged upstream of the first compressor wheel, wherein the supercharging device is configured to supply the branched-off air to the second compressor wheel such that the second compressor wheel and, via the second compressor wheel, the electric machine, is drivable by the branched-off air.

2. The supercharging device according to claim 1, wherein the electric machine is driven by the branched-off air via the second compressor wheel and is thus operable as a generator, by which mechanical energy provided by the second compressor wheel is converted into electrical energy.

3. The supercharging device according to claim 1, wherein the overrun air recirculation device has at least one return line which is flowed through by the branched-off air and in which the second compressor wheel is arranged.

4. The supercharging device according to claim 3, wherein in a first operating state, the branched-off air flows through the return line in a first direction.

5. The supercharging device according to claim 4, wherein in a second operating state, in which the second compressor wheel compresses the air for feeding to the internal combustion engine, the air for feeding to the internal combustion engine flows through the return line in a second direction which is opposite to the first direction.

6. The supercharging device according to claim 2, further comprising: a valve device by which respective flows of air through the return line are adjustable.

7. A method for operating a supercharging device for an internal combustion engine of a motor vehicle, the supercharging device having an exhaust-gas turbocharger with a turbine wheel drivable by exhaust gas and with a first compressor wheel drivable by the turbine wheel, the supercharging device further having an electric compressor with an electric machine and a second compressor wheel drivable by the electric machine, the method comprising the steps of: in an event of a load reduction of the internal combustion engine, branching-off a portion of air compressed by the first compressor wheel at a first point arranged downstream of the first compressor wheel and returning the air from the first point to a second point arranged upstream of the first compressor wheel; and in at least one operating state, supplying the branched-off portion of air to the second compressor wheel such that the second compressor wheel and, via the second compressor wheel, the electric machine, are driven by the branched-off air.

8. The method according to claim 7, further comprising the step of: operating the electric machine as a generator that converts mechanical energy provided by the second compressor wheel into electrical energy, wherein the electric machine is driven by the branched-off portion of air via the second compressor wheel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 is a schematic illustration of a supercharging device according to the invention as per a first embodiment for an internal combustion engine of a motor vehicle.

[0025] FIG. 2 is a schematic illustration of the supercharging device according to the invention as per a second embodiment.

[0026] In the figures, identical or functionally identical elements are denoted by the same reference designations.

DETAILED DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 shows, in a schematic illustration, a first embodiment of a drive device, denoted as a whole by 1, for a motor vehicle, in particular for a motor car such as for example a passenger motor car. Here, the drive device 1 comprises an internal combustion engine 2, which is designed for example as a reciprocating-piston engine. The internal combustion engine 2 has an engine housing 3 which is formed for example as a cylinder housing, in particular as a cylinder crankcase, and by means of which multiple combustion chambers 4 in the form of cylinders are formed. Furthermore, the drive device 1 comprises a supercharging device 5, by means of which the internal combustion engine 2, in particular the combustion chambers 4, can be supplied with compressed air. Here, the drive device 1, in particular the supercharging device 5, comprises an intake tract 6 which can be flowed through by air and by means of which the air can be conducted to and in particular into the combustion chambers 4. The internal combustion engine 2 can thus be supplied with said air by way of the intake tract 6. The combustion chambers 4 are supplied with air compressed by the supercharging device 5 and with fuel, in particular liquid fuel, for the operation of the internal combustion engine 2, such that a fuel-air mixture forms in the respective combustion chamber 4. The fuel-air mixture is burned, resulting in exhaust gas of the internal combustion engine 2. Here, an exhaust tract 7 is provided which can be flowed through by the exhaust gas of the internal combustion engine 2 and by which the exhaust gas can be discharged from the combustion chambers 4. In the intake tract 6, there is arranged an air filter 8 by which the air that has initially not yet been compressed is filtered.

[0028] The supercharging device 5 comprises at least one exhaust-gas turbocharger 9, which has a compressor 10 arranged in the intake tract 6 and a turbine 11 arranged in the exhaust tract 7. The turbine 11 comprises a turbine wheel 12, which can be driven by the exhaust gas of the internal combustion engine 2. The compressor 10 comprises a first compressor wheel 13, which is arranged in the intake tract 6 and which can be driven by the turbine wheel 12. Here, the turbine wheel 12 and the compressor wheel 13 are constituent parts of a rotor 14 of the exhaust-gas turbocharger 9. The rotor 14 also comprises a shaft 15, by means of which both the compressor wheel 13 and the turbine wheel 12 are connected for conjoint rotation. In this way, the compressor wheel 13 can be driven by the turbine wheel 12 via the shaft 15. By virtue of the compressor wheel 13 being driven, air that is fed to the combustion chambers 4 is compressed by the compressor wheel 13, wherein the compressed air is also referred to as charge air.

[0029] Furthermore, an electric compressor 16 is provided which has a second compressor wheel 17 and an electric machine 18. The electric machine 18 has a stator (not shown in FIG. 1) and a rotor which is rotatable about an axis of rotation 19 relative to the stator. Here, the rotor comprises a shaft 20 which is rotatable about the axis of rotation 19 and to which the second compressor wheel 17 is connected for conjoint rotation. Here, the second compressor wheel 17 can be electrically driven by the electric machine 18 via the shaft 20. By virtue of the compressor wheel 17 being driven in this way, the compressor wheel 17 is rotated about the axis of rotation 19, and air that is fed to the combustion chambers 4 is compressed by the compressor wheel 17. For example, the compressor wheels 13 and 17 are connected or arranged in parallel with respect to one another, such that the compressor wheels 13 and 17 can for example be operated in parallel with respect to one another. In particular, it is contemplated for at least a first of the combustion chambers 4 to be supplied with compressed air by the compressor wheel 13 and, in parallel, for at least a second of the combustion chambers 4, which differs from the first combustion chamber, to be supplied with compressed air by the compressor wheel 17.

[0030] To be able to prevent the so-called compressor surging of the compressor wheel 13 or of the compressor 10, the first compressor wheel 13 or the compressor 10 is assigned an overrun air recirculation device 21, by which, in the event of a load reduction of the internal combustion engine 2, at least a part of the air compressed by way of the compressor wheel 13 can be branched off from the intake tract 6 at a first point S1 arranged downstream of the first compressor wheel 13 and can be returned from the first point Si to a second point S2 arranged upstream of the first compressor wheel 13. In other words, if for example a load reduction of the internal combustion engine 2 occurs, wherein the load reduction is also referred to as a load dump, then the air compressed by way of the compressor wheel 13 is branched off from the intake tract 6, and is for example introduced into a return line 22 of the overrun air recirculation device 21, at the first point S1. The return line 22 is fluidically connected at the point S1 and S2 fluidically to the intake tract 6, in particular to an air line 23 of the intake tract 6, such that, for example at the point 51, the air compressed by the compressor wheel 13 can flow out of the intake tract 6 or out of the air line 23 and into the return line 22. The branched-off air that flows through the return line 22 is returned from the first point S1 to the second point S2 by means of the return line 22 and can, at the second point S2, flow out of the return line 22 and into the intake tract 6 or into the air line 23. In this way, it is for example the case that the branched-off air is recycled or the branched-off air can recirculate, because the branched-off air can flow from the point S2 to the compressor wheel 13 and be compressed again by means of the compressor wheel 13.

[0031] For example, the air is compressed to a charge pressure by the compressor wheel 13. As a result of the air compressed by the compressor wheel 13 being branched off and returned, a depletion of the charge pressure can be realized, such that compressor surging of the compressor 10 can be avoided. The depletion of the charge pressure is also referred to as charge pressure depletion. During the charge pressure depletion, it is for example the case that the branched-off air that flows through the return line 22 is expanded.

[0032] Since the internal combustion engine 2 is equipped with the supercharging device 5, the internal combustion engine 2 is also referred to as a turbo engine. In the case of such a turbo engine, it is desirable for a feed of air into the combustion chambers 4 to be reduced as quickly as possible in the event of a load dump, and thus for the abovementioned charge pressure depletion to be performed particularly quickly. The load dump and thus the reduction of the feed of air take place for example by virtue of a throttle flap 24 that is arranged in the intake tract 6 being at least partially closed. Here, the throttle flap 24 is arranged downstream of the compressor wheels 13 and 17 and upstream of the combustion chambers 4 and is utilized to adjust a quantity or mass of the air for feeding to the combustion chambers 4. Here, the charge pressure depletion is performed in front of or upstream of the throttle flap 24 and in particular by way of a backward flow of the air compressed by the compressor wheel 13 for example via the compressor wheel 13 counter to an intake flow direction.

[0033] This can conventionally lead to acoustic anomalies, whereby corresponding vehicle requirements can no longer be adhered to. Furthermore, it is conventionally the case that energy contained in the compressed and branched-off air is lost without being utilized. The higher the load pressure in the event of the load dump, the longer the load pressure depletion lasts, and the more likely acoustic anomalies are. For this reason, the overrun air recirculation device 21 is used, which conventionally has an overrun air recirculation valve. By means of the overrun air recirculation device 21, the backflow, provided for the charge pressure depletion, of the air compressed by the compressor wheel 13 via the compressor wheel 13 counter to the intake flow direction can be avoided, because the compressed air can be returned via the return line 22. Here, the branched-off and returned air bypasses the compressor wheel 13, such that the branched-off air that is returned to the point S2 does not flow through or via the compressor wheel 13. However, in the case of conventional supercharging devices utilizing an overrun air recirculation device, energy contained in the branched-off, compressed air is lost without being utilized. This can however now be avoided with the supercharging device 5.

[0034] To now realize particularly efficient and energy-conserving operation, the supercharging device 5 is designed to supply the branched-off air to the second compressor wheel 17, such that the second compressor wheel 17 and, via the second compressor wheel 17, the electric machine 18 are drivable or are driven by the branched-off air flowing through the return line 22. In other words, in at least one first operating state, the second compressor wheel 17 is supplied with the air compressed by means of the compressor wheel 13, such that the second compressor wheel 17 and, via the second compressor wheel 17, the electric machine 18 are driven by the branched-off air compressed by the compressor wheel 13.

[0035] In the case of overrun air recirculation valves that are conventionally used, the charge pressure depletion is performed by recycling of the charge air via the compressor 10. For this purpose, the compressed charge air is conducted via the overrun air recirculation valve back to the point S2 and is expanded in the process, wherein the point S2 is arranged in a low-pressure region of the intake tract 6. By contrast, the point S1 is arranged in a high-pressure region of the intake tract 6, because a higher pressure prevails at the point S1 than at the point S2. After the return of the compressed air to the point S2, the air is compressed again by means of the compressor 10. Here, the charge pressure depletion takes place relatively slowly, and the energy contained in the air compressed by means of the compressor wheel 13 is not utilized further, or is converted primarily into heat. By contrast, in the case of the supercharging device 5, energy recovery is provided. In the context of the energy recovery, the compressor wheel 17 and, via this, the electric machine 18 are driven by the branched-off air flowing through the return line 22.

[0036] In at least one second operating state that differs from the first operating state, the electric machine 18 is operated for example in a motor mode and thus has an electric motor. For this purpose, the electric machine 18 is for example supplied with electrical energy or electrical current that is stored in an energy store not shown in FIG. 1. By operation of the electric machine 18 in the motor mode, the compressor wheel 17 is driven by the electric machine 18 and is thus rotated in a first direction of rotation about the axis of rotation 19, whereby air that flows through the return line 22 is compressed and fed to the combustion chambers 4.

[0037] In the abovementioned first operating state, however, the compressor wheel 17 is driven by air that is or has been compressed by means of the compressor wheel 13 and flows through the return line 22. In this way, energy contained in the branched-off air is converted into mechanical energy, which is provided by the compressor wheel 17. In this way, the electric machine 18 is driven by the compressor wheel 17 via the shaft 20. In the first operating state, the electric machine 18 is operated in a generator mode and thus as a generator, which converts at least a part of the mechanical energy provided by the compressor wheel 17 into electrical energy and provides this electrical energy. Here, in the first operating state, the compressor wheel 17 rotates about the axis of rotation 19 in a second direction of rotation that is opposite to the first direction of rotation. Thus, in the first operating state, the compressor wheel 17 functions as a turbine or as a turbine wheel, by means of which the electric machine 18, in particular the rotor or electric machine 18, is driven. By means of the compressor wheel 17, the branched-off air is expanded, which can then flow into the air line 23 at the second point S2 and finally flow back to the compressor wheel 13.

[0038] To realize the first operating state, in the event of the load dump, the backed-up charge air is conducted via the compressor wheel 17 and thus via the electric compressor 16 to the low-pressure region and expanded. This is realized for example by means of corresponding valve switching in the intake tract 6. In other words, a valve device 25 is preferably provided by which respective flows of air through the return line 22 and through the air line 23 are adjustable. In other words, it is for example possible by means of the valve device 25 to switch over between the stated operating states, which are also referred to as operating modes.

[0039] Altogether, it is evident that, in the event of a load dump, energy in the form of electrical current can be obtained from the charge air compressed by the compressor wheel 13. In relation to a conventional overrun air recirculation valve, it is furthermore possible for disturbing acoustic noises to be avoided or to be kept particularly low, for example because the charge pressure depletion can be performed particularly quickly and advantageously. In particular, the charge pressure depletion can be better controlled in open-loop or closed-loop fashion in relation to conventional overrun air recirculation valves, whereby the generation of undesired noises can be avoided. Thus, with the supercharging device 5, a particularly advantageous recuperation of energy contained in the air compressed by means of the compressor wheel 13, and a particularly fast charge pressure depletion in the event of a load dump, can be realized.

[0040] FIG. 2 shows a second embodiment of the supercharging device 5. In the first embodiment, at least a part of the air flowing through the intake tract 6 is branched off in front of the first compressor wheel 13 or upstream of the first compressor wheel 13. The branched-off air or the branched-off part is not compressed by the compressor wheel 13, but is rather fed to the second compressor wheel 17 and compressed by the compressor wheel 17 or by the electrical compressor 16, such that, for example, the compressors 10 and 16 operate in parallel.

[0041] In the second embodiment, however, it is for example the case that series operation of the compressors 10 and 16 is provided. For this purpose, in particular in a supercharging mode that is illustrated in FIG. 2 by arrows 28, the air flowing through the intake tract 6 is firstly compressed by means of the compressor wheel 13. At least a part of the air compressed by means of the compressor wheel 13 is fed to the compressor wheel 17 via a line 30 and is compressed once again or further by means of the compressor wheel 17. Here, a check valve 26 ensures that the air compressed by means of the compressor wheel 17 cannot flow back to the first compressor wheel 13. Here, the line 30 is fluidically connected to a first air line, which leads away from the compressor wheel 13, at a point arranged downstream of the compressor wheel 13. Furthermore, the line 30 is fluidically connected to a second air line, which leads to the compressor wheel 17, at a point arranged downstream of the compressor wheel 13. In this way, by means of the line 30, at least the stated part of the air compressed by means of the compressor wheel 13 can be branched off from the first air line and introduced to or into the second air line. The branched-off part is then conducted by means of the second air line to the compressor wheel 17. Here, in particular during the supercharging mode, a valve 27 arranged in the line 30 is opened.

[0042] In FIG. 2, arrows 29 illustrate the above-described charge pressure depletion. During the charge pressure depletion, a flow cross section of the intake tract 6 that can be flowed through by the air is at least reduced or at least partially shut off by virtue of the throttle flap 24 being at least partially closed. In this way, the feed of air to the combustion chambers 4 is reduced, in particular in relation to the supercharging mode that precedes the charge pressure depletion. Additionally, the overrun air recirculation device 21, in particular the overrun air recirculation valve thereof, is then opened, and the valve 27 arranged in the line 30 is closed, in order that the air flows via the compressor wheel 17 and thus via the electric compressor 16, such that the electric machine 18 of the electric compressor 16 can be operated in the generator mode in the described manner.

LIST OF REFERENCE DESIGNATIONS

[0043] 1 Drive device [0044] 2 Internal combustion engine [0045] 3 Engine housing [0046] 4 Combustion chamber [0047] 5 Supercharging device [0048] 6 Intake tract [0049] 7 Exhaust tract [0050] 8 Air filter [0051] 9 Exhaust-gas turbocharger [0052] 10 Compressor [0053] 11 Turbine [0054] 12 Turbine wheel [0055] 13 First compressor wheel [0056] 14 Rotor [0057] 15 Shaft [0058] 16 Electric compressor [0059] 17 Second compressor wheel [0060] 18 Electric machine [0061] 19 Axis of rotation [0062] 20 Shaft [0063] 21 Overrun air recirculation device [0064] 22 Return line [0065] 23 Air line [0066] 24 Throttle flap [0067] 25 Valve device [0068] 26 Check valve [0069] 27 Valve [0070] 28 Arrow [0071] 29 Arrow [0072] 30 Line [0073] S1 First point [0074] S2 Second point

[0075] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.