Abstract:
A drive unit for a motor vehicle includes an internal combustion engine having a feeder line for feeding combustion air to the internal combustion engine and a compressor device that cooperates with the feeder line and by means of which the combustion air is compressed for the internal combustion engine. A bypass line opens into the feeder line, and through which the combustion air can be fed to the internal combustion engine without passing through the compressor device. An isolating mechanism associated with the bypass line serves to shut off and/or adjust the quantity of combustion air that flows through the bypass line. A control unit controls the isolating mechanism in such a manner that the isolating mechanism is at least partly closed or is caused to at least partly close when the internal combustion engine is in coasting mode.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application No. 202015004831.5, filed Jul. 7, 2015, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present disclosure pertains to a drive unit for a motor vehicle and a motor vehicle having a drive unit of such kind. The present disclosure relates further to a computer software product for controlling the drive unit. 
       BACKGROUND 
       [0003]    Modern drive units include an internal combustion engine, for example a four-stroke gasoline or Diesel engine, in which the combustion air is compressed to a pressure greater than atmospheric pressure to improve performance. Depending on the variant, the drive unit includes one or more, typically two compression stages. Drive units with one compression stage are usually equipped with a turbocharger device or a compressor device including a compressor. Drive units with two compression stages include either two turbocharger devices or a turbocharger device and a compressor device. The compressor device may include a rotary compressor in the form of a Roots-type supercharger, for example. Whereas the turbocharger device is driven by the exhaust gas enthalpy of the exhaust gases in the internal combustion engine, the compressor device is driven either by the internal combustion engine itself or by means of an electric motor. Internal combustion engines in which the combustion air is compressed are often also called “forced induction” internal combustion engines. 
         [0004]    If the compressor device is driven by the internal combustion engine itself, the compression performance provided by the compressor increases with the speed of the internal combustion engine. In this case, a coupling device may be provided, with which the compressor device can be coupled to the internal combustion engine or uncoupled therefrom depending on the speed of the internal combustion engine, At low engine speeds, the compressor device delivers only a fraction of its compression capability, as a result of which the torque output from the internal combustion engine is low at low engine speeds. Since the turbocharger device&#39;s compression performance depends on the pressure in the discharge line, which also increases with the speed of the engine, the output even from internal combustion engines with two-stage supercharging is low at low engine speeds, which is particularly noticeable as a negative phenomenon during an acceleration operation. Accordingly, this behavior is referred to as poor response behavior of the internal combustion engine. 
         [0005]    Particularly in high-performance engines, the compressor device must have relatively large dimensions in order to cover a sufficiently wide operating area. However, as the compressor becomes larger, a not inconsiderable portion of the torque delivered by the internal combustion engine is required to drive the compressors, which not only exacerbates the drawback of weak torque at low engine speeds described previously, but also increases fuel consumption. 
         [0006]    If the compressor device is driven by an electric motor, the speed of the compressor can be set and altered independently of the speed of the internal combustion engine. In this case, it is not absolutely necessary to arrange a coupling device between the compressor and the electric motor. When an electric motor is used, the response behavior of the internal combustion engine can he improved, but then the electric motor must supply a certain output to bring the compressor up to the optimal speed, thus entailing increased consumption of electrical energy. Since the electrical energy is provided by a generator, which is driven by the internal combustion engine, the increased consumption of electrical energy also causes increased fuel consumption. 
         [0007]    Particularly given the ongoing efforts to lower CO 2  emissions, increased fuel consumption by internal combustion engines with one or two compression stages is undesirable. 
       SUMMARY 
       [0008]    The present disclosure is directed to a drive unit having one or two compression stages. The internal combustion engine not only delivers good torque output even at low engine speeds, and thus also exhibiting good response behavior, but can also be operated with reduced fuel consumption. 
         [0009]    One embodiment of the drive unit for a motor vehicle is equipped with an internal combustion engine, a feeder line for feeding combustion air to the internal combustion engine, a compressor that cooperates with the feeder line, and which is usable for compressing the combustion air for the internal combustion engine, and a bypass line that opens into the feeder line and through which the combustion air can be fed to the internal combustion engine without passing through the compressor device. An isolating mechanism is assigned to the bypass line and serves to close off and/or adjust the quantity of combustion air flowing through the bypass line. A control unit controls the isolating mechanism in such a manner that the isolating mechanism is at least partly closed or is caused to partly close when the internal combustion engine is in a coasting mode. 
         [0010]    Coasting mode, also referred to as freewheeling, is defined as follows. The internal combustion engine and the drive unit are in coasting mode when the motor vehicle is travelling and the internal combustion engine is engaged, that is to say the engine is connected to the drivetrain via the main coupling, but the driver does not actuate the gas pedal. In coasting mode, fuel is not injected into the cylinders, because the internal combustion engine does not need to transmit aloud. The pistons in the internal combustion engine move under the effect of the mass inertia of the motor vehicle, so combustion air is drawn in. The control unit detects that the internal combustion engine and the drive unit are in coasting mode. To do this, the control unit is able to cooperate with sensors, which capture the speed of the motor vehicle or the coupling state of the main coupling in the motor vehicle&#39;s drivetrain for example. 
         [0011]    In conventional drive units, the isolating mechanism is open in coasting mode, which means that the combustion air flows through the bypass line, not through the compressor device, no the load is removed from the compressor device. Consequently, the combustion air is not compressed, and it does not need to be because an air-fuel mixture for ignition is not being produced anyway, and the internal combustion engine does not need to transfer any load. In contrast to this, according to the present disclosure, the isolating mechanism is at least partly and in particular completely or substantially completely closed when the internal combustion engine is in coasting mode, so that at least some of the combustion air flows through the compressor device. If the isolating mechanism is already partly and in particular completely or substantially completely closed, this state is maintained. Consequently, the enthalpy in the combustion air acts on the compressor device, causing the speed of the compressor device to increase. When the internal combustion engine is switched from coasting mode to partial or full load operation and is required to transfer load, compressed combustion air is available immediately, the compressor device does not first have to he accelerated to a speed at which it was previously running in coasting mode due to the effect of the enthalpy of the combustion air. The response behavior of the internal combustion engine is improved with respect to that of known drive units. Since the power for increasing the rotating speed does not have to be supplied by either the internal combustion engine or the electric motor, fuel consumption and consequently CO 2  emissions are also reduced. 
         [0012]    A refinement of the drive unit as suggested is characterized in that the drive unit is equipped with a throttle valve allocated to the internal combustion engine, which valve cooperates with the feeder line, and the control unit controls the throttle valve in such a manner that the throttle valve is at least partly open or at least partly opened when the internal combustion engine is in coasting mode and the isolating mechanism is at least partly closed. 
         [0013]    The throttle valve serves to alter the quantity of combustion air that flows through the feeder line to the internal combustion engine, thereby altering the load on the internal combustion engine. In conventional drive units, the throttle valve is at least partly closed in coasting mode, since the internal combustion engine does not have to transfer any load. In contrast to this, according to the present disclosure, the throttle valve is at least partly, particularly completely or substantially completely open in coasting mode, If said valve is at already least partly, particularly completely or substantially completely open, this state is maintained. This ensures that the flow of combustion air through the feeder line to the internal combustion engine is disturbed as little as possible by the throttle valve. The wider the throttle valve is opened, the less the flow of combustion air is disturbed. Consequently almost all of the enthalpy of the combustion air is available for increasing the speed of the compressor device, and its speed in coasting mode can be increased further. 
         [0014]    A further variant relates to a drive unit for a motor vehicle particularly according to one of the preceding variations, including an internal combustion engine, a feeder line for feeding combustion air to the internal combustion engine, a compressor device that cooperates with the feeder line, and by means of which the combustion air for the internal combustion engine is compressible, bypass line that opens into the feeder line and through which the combustion air may be fed to the internal combustion engine without passing through the compressor device. An isolating mechanism is assigned to the bypass line and serves to close off and/or adjust the quantity of combustion air flowing through the bypass line, and having a control unit with which the isolating mechanism may be controlled. The control unit acts in controlling manner on the isolating mechanism in such a manner that the isolating mechanism is at least partly closed or is caused to at least partly close when the internal combustion engine is operated below or at full suction load. 
         [0015]    Full suction load is understood to mean a full load state reached by an internal combustion engine which is reached without forced induction or at least substantially without forced induction or with negligible forced induction of the combustion air that is fed to the internal combustion engine. The drive units that are usually used for the compressor device such as the internal combustion engine itself or an electric motor are not active and/or are decoupled. 
         [0016]    In this embodiment as well, the isolating mechanism may be completely, substantially completely or partly closed or caused to close. If it has already been partly closed, this state is maintained. This enables at least a portion of the combustion air to flow through the compressor device even below or at the full suction load of the internal combustion engine, to that the enthalpy in the combustion air can he used to increase the speed of the compressor device. This also provides the advantages described previously of reduced fuel consumption with improved response behavior of the internal combustion engine in coasting mode. 
         [0017]    In a variant, the control unit acts on the isolating mechanism in such a manner that in coasting mode or when the internal combustion engine is operating below or at its full suction load the isolating mechanism is at least partly opened, for example completely or substantially completely opened, when the quantity of combustion air fed to the internal combustion engine exceeds a predetermined value. The quantity of combustion air supplied to the internal combustion engine may be recorded by flowmeter or a pressure sensor, for example. As was described earlier, the isolating mechanism s completely or partly closed below or at full suction load. Consequently, at least a portion of the combustion air flows through the compressor device and is compressed there. In this circumstance, however, the danger arises that the compressor device, and particularly the rotating compressor may reach an excessively high rotating speed, which may result in damage to the compressor device. To avoid this, the isolating mechanism is opened when a predetermined quantity of combustion air is exceeded, so that at least a portion of the combustion air flows through the bypass line and so does not contribute to an increase in rotating speed. 
         [0018]    In a further development, the drive unit is equipped with a throttle valve, which is allocated to the internal combustion engine, and which cooperates with the feeder line and is moved between an open position and a closed position. The control unit controls the throttle valve in such a manner that the throttle valve is moved towards its closed position, and is completely or substantially closed for example when the internal combustion engine is in coasting mode or operating below or at its full suction load, if the quantity of combustion air supplied to the internal combustion engine exceeds a predetermined value. In this context, the throttle valve may be the same as the valve described previously. However, it is also possible to provide another throttle valve in addition to or instead of the throttle valve described previously. The term open position understood to describe the position of the throttle valve in which it has opened completely. Similarly, the term closed position is understood to refer to position of the throttle valve in which it is closed as completely as possible. When the internal combustion engine is operating, the throttle valve in the closed position is typically not completely closed, since otherwise the internal combustion engine would stall. in the closed position, however, the internal combustion engine does not transfer any load. 
         [0019]    The movement of the throttle valve towards its closed position has the effect of constricting the cross section of the feeder line inside the throttle valve through which the compression air can flow. Consequently, the quantity of combustion air that flows through the feeder line is also reduced. The quantity of combustion air flowing through the feeder line is reduced substantially by a reduction of the flow velocity of combustion air caused by a throttle valve. In this way too, the compressor device is prevented from increasing to speeds that might cause damage. 
         [0020]    In a further variant, the compressor device is driven by the internal combustion engine and/or by a further drive unit, particularly an electric motor. At least one coupling device is provided to decouple the compressor device from the internal combustion engine and/or the further drive unit. The capability to decouple the compressor device from the internal combustion engine or the further drive unit and couple it therewith again has the effect of enabling the compressor device to be adapted to the respective operating state of the internal combustion engine at the time of coupling or decoupling. If the compressor device is driven by the internal combustion engine itself, the speed of the internal combustion engine and the speed of the compressor device are in a fixed ratio to one another. Depending on the transmission ratio, given a low speed of the internal combustion engine, it may be that the compressor device rotates at a speed that is too low to produce detectable compression. In such a case, the torque the internal combustion engine has to transfer to the compressor device is not being used optimally, and the response behavior of the internal combustion engine is deteriorated. The coupling device makes it possible for the compressor device not to be coupled until the rotating speed delivered by the internal combustion engine is fast enough to produce detectable compression. The response behavior of the internal combustion engine is improved due to the fact that the internal combustion engine reaches the rotating speed range at which it outputs maximum torque more quickly, since the compressor device does not have to be accelerated at the same time. 
         [0021]    In a further variant, the control unit controls the coupling device in such a manner that the compressor device is or can be at least partly decoupled from the internal combustion engine and/or the further drive unit when the internal combustion engine is in coasting mode or when the internal combustion engine is operated below or at its full suction load. Both in coasting mode and when operated at or below full suction load, the compressor device is at least decoupled from the internal combustion engine or, if the compressor device has already been at least decoupled, the decoupled state is maintained. In particular, the compressor device is decoupled completely or substantially completely. The same also applies if the compressor device is driven by an electric motor or a further drive unit. In the decoupled state, the compressor device can rotate freely, detached from the components that may be connected to it via the coupling device, particularly the drive units thereof. Consequently, the compressor device is not required to accelerate the components that may be connected to it, so that the enthalpy in the combustion air may be used entirely to accelerate the compressor device and bring it to a faster rotating speed. This also represents a further contribution to improving the internal combustion engine&#39;s response behavior will at the same time economizing on fuel. 
         [0022]    If the compressor device is driven by the internal combustion engine, the compressor device is not coupled with it until the internal combustion engine is being operated at a sufficiently high rotating speed. Special rotation ratios are not necessary. The coupling device undergoes a soft startup, so the compressor device is not subjected to a sudden change of speed. Consequently, the internal combustion engine only has to accelerate the compressor device by a relatively small amount, In this way, although only to a very small degree, the compressor device assists the internal combustion engine in accelerating the motor vehicle, since the compressor device transfers a torque to the internal combustion engine until a certain point after coupling. Only after that point does the internal combustion engine transfer the torque to the compressor. To this extent, the compressor device functions as a flywheel in a very limited way, and stores the enthalpy in the combustion air in the form of rotating energy due to the mass inertia of the rotating parts. 
         [0023]    If the compressor device is driven by an electric motor, the electric motor may be switched currentless in coasting mode or until full suction load is reached, the effect of which is that the compressor device turns the rotor of the electric motor as well. In this case, the enthalpy of the combustion air must also be used to accelerate the rotor as well, but this becomes less disadvantageous as the size and weight of the rotor become smaller. However, the larger the electric motor becomes, and accordingly the heavier the rotor, the more advantageous it becomes to use the compressor device with electric motors as well. If the compressor device is decoupled from the electric motor and the rotor, the rotor is not caused to rotate in coasting mode or until full suction load, and consequently all or practically all of the enthalpy in the combustion air is available for increasing the rotating speed of the compressor device, so the provision of the coupling device makes it possible to bring the compressor device to higher speeds than without a coupling device, The effects of improved response behavior with reduced fuel consumption are amplified in this way. 
         [0024]    In a further variant, the drive unit includes a turbocharger device with a turbocompressor and an exhaust gas turbine that drives the turbocompressor, the turbocompressor cooperates with the feeder line, and is disposed upstream of the compressor device and/or the bypass line when seen in direction of supply of the combustion air, the exhaust gas turbine is arranged in a discharge line of the drive unit, a waste gate line is provided that opens into the discharge line, and via which the exhaust gas may be discharged without passing through the exhaust gas turbine, and an additional isolating mechanism is assigned to the waste gate line, which mechanism serves to shut off and/or adjust the quantity of exhaust gas that flows through the waste gate line. 
         [0025]    The combination of compressor device and turbocharger device makes even greater compression values achievable, and therefore the internal combustion engine can be operated with yet greater loads. Since two differently driven compressor types are used, each of which reaches its optimum compression value at different speeds of the internal combustion engine, overall a more uniform compression over the rotating speed range of the internal combustion engine is achieved. The rotating speed of the turbocharger device depends on the exhaust gas enthalpy contained in the exhaust gas. It is also possible with the aid of the waste gate line to alter the quantity of exhaust gas that flows through the waste gate line and the exhaust gas turbine. This represents another way to adjust the rotating speed of the turbocompressor with certain limits. 
         [0026]    In a further development of the drive unit, the control unit controls the additional isolating mechanism in such way that the additional isolating mechanism is at least partly closed or caused to partly close when the internal combustion engine is in coasting mode or when the internal combustion engine is operated below or at full suction load. in this context, the additional isolating mechanism may be completely, substantially completely or partly closed. If it is already completely or partly closed, this state is maintained. This enables a larger quantity of exhaust gas to be delivered to the exhaust gas turbine, leading to an increase in the speed of the turbocompressor and greater compression of the combustion. Accordingly, a greater quantity of combustion air then flows through the compressor device, so that the compressor device may be brought to a faster rotating speed than without the turbocharger device. This in turn further improves the response behavior of the internal combustion engine. 
         [0027]    The drive unit is developed further to the effect that the control unit controls the isolating mechanism in such a manner that the additional isolating mechanism is at least partly closed or caused to at least partly close when the isolating mechanism is at least partly closed. In particular, the isolating mechanism is completely or substantially completely closed when the additional isolating mechanism is completely or substantially completely closed or caused to completely or substantially completely close. The more completely the additional isolating mechanism is closed, the more exhaust gas flows through the exhaust gas turbine, which in turn increases the speed of the turbocompressor. The faster the turbocompressor turns the more intensely the combustion air is compressed. Since at the same time the isolating mechanism is at least partly closed, some of the compressed combustion air flows through the compressor device and brings it to a fast rotating speed. In this way, it is possible to influence the speed of the compressor device via the isolating mechanism and the additional isolating mechanism. 
         [0028]    In another variant of the drive unit, the control unit controls the additional isolating mechanism in such a manner that when the internal combustion engine is in coasting mode or the internal combustion engine is operated below or at its full suction load the additional isolating mechanism at least partly open when the quantity of combustion air delivered to the internal combustion engine exceeds a predetermined value or the predetermined value. In particular, the additional isolating mechanism is completely or substantially completely opened. As was described previously, when the drive unit is operated it may happen that the speed of the compressor device increase to such a point that the compressor device can be damaged. Because the additional isolating mechanism is completely or partly opened, some of the exhaust gas flows through the waste gate line, thereby reducing the rotating speed of the turbocompressor. As a direct consequence of this, the combustion air undergoes less intense compression, thereby causing the speed of the compressor device to fall below a dangerous value, or preventing the speed from rising to a dangerous value at all. Moreover, opening the additional isolating mechanism also serves to prevent the exhaust gas turbine and the turbocompressor from increasing to a damaging value. 
         [0029]    From the preceding notes it will be evident that that the compressor device may be exposed to the enthalpy in the combustion air for as long as possible, in order to increase the rotating the speed of the compressor device as far as possible. Since only the enthalpy that is contained in the combustion air anyway is used for this, neither the internal combustion engine nor the electric motor or any further drive unit of the compressor device needs to provide the output necessary for this, which in turn results in reduced fuel consumption. Since the compressor device is brought to the corresponding rotating speed in coasting mode or at or below its full suction load, the compression achieved thereby is available immediately, particularly when switching to full load operation. Thus it is no longer necessary to wait until the compressor device has been accelerated to said rotating speed, so that the response behavior of the internal combustion engine is improved and the motor vehicle is accelerated more quickly. 
         [0030]    A controller for the purposes of the embodiments of the present disclosure described previously may be in the form of hardware and/or software, for example as a software program or software program module. The pressure sensor may also be in the form of hardware and/or software, for example as a software program or software program module for the purposes of the embodiments of the present disclosure described previously. 
         [0031]    The controller, control unit and/or pressure sensors may particularly each be equipped with a digital processing unit or a shared digital processing unit, which preferably includes a microprocessor unit (CPU). The CPU may be connected to a storage system and/or a bus system by a data and/or signal link. Further, the controller may be equipped individually with or share one or more programs or program modules. The digital processing unit may be constructed in such a manner that commands which are implemented as a program stored in a storage system are processed in sequence, input signals are received by a data bus system and/or output signals are forwarded to a data bus system. A storage system may include one or more, particularly different, storage media. The storage media may particularly be optical, magnetic, solid state and/or other, preferably non-volatile storage media. 
         [0032]    A drive unit for the purposes of the embodiments described previously may also include control means, which may be understood to be function module architecture. Such a function module architecture includes at least one function block, so that a control system of the drive unit amounts to a device having means for carrying out a procedure that is defined by the mode of operation of the drive unit. In this context, the control system, which includes the control unit and/or the pressure sensor for example, corresponds to the function block described. 
         [0033]    A further aspect relates to a motor vehicle having a drive unit according to one of the embodiments described in the preceding text. The technical effects and advantages that are to be gained with the motor vehicle as suggested correspond to those that have been discussed with regard to the drive unit as suggested. In summary, the reduced fuel consumption with better response behavior of the internal combustion engine is particularly notable. 
         [0034]    A further aspect relates to a computer software product with a software code which is stored on a computer-readable medium and designed for controlling the isolating mechanism, an additional isolating mechanism and/or the throttle valve of a drive unit according to one of the aforementioned embodiments. The isolating mechanism is caused to at least partly close, in particular a drive unit of the compressor device is also switched off or at least partly decoupled when the internal combustion engine is in a coasting mode and/or the internal combustion engine is operated below or at its full suction load. With the computer software product, it is possible to control the drive unit in such a manner that fuel consumption is reduced and the response behavior of the internal combustion engine is improved. 
         [0035]    In a variant of the computer software product, the throttle valve is at least partly opened in coasting mode and when the isolating mechanism is at least partly closed. The wider the throttle valve is opened, the more smoothly the combustion air is able to flow through the feeder line, which enables the compressor device to reach particularly high rotating speeds, thus in particular lending a noticeable improvement to the response behavior of the internal combustion engine. 
         [0036]    In an alternative variant of the computer software product, when the internal combustion engine is operated below or at its full suction load, the isolating mechanism is at least partly opened and/or the throttle valve may be moved towards its closed position if the quantity of combustion air being fed to the internal combustion engine exceeds a predetermined value. This serves to prevent the speed of the compressor device from reaching values at which the compressor device might be damaged. 
         [0037]    In a refinement of the computer software product, in which the drive unit is a turbocharger device equipped with a turbocompressor and an exhaust gas turbine that drives the turbocompressor, the turbocompressor cooperates with the feeder line and is located upstream of the compressor device and/or the bypass line viewed in the feed direction of the combustion, the exhaust gas turbine is arranged in a discharge line of the drive unit, a waste gate line opening into the discharge line is provided, via which the exhaust gas may be discharged without passing through the exhaust gas turbine, and an additional isolating mechanism is assigned to the waste gate line and is used to shut off and/or adjust the quantity of exhaust gas that flows through the waste gate line. 
         [0038]    The additional isolating mechanism is at least partly closed when the internal combustion engine is in coasting mode or the internal combustion engine is operated below or at its full suction load. In particular, the additional isolating mechanism is completely or substantially completely closed. The effect of this is that a greater quantity of exhaust gas is fed to the exhaust gas turbine, thereby increasing the speed of the turbocompressor and leading to more intense compression of the combustion air, Consequently, a greater quantity of combustion air passes through the compressor device, so that the compressor device may be brought to a faster rotating speed than without the turbocharger device. This in turn further improves the response behavior of the internal combustion engine. 
         [0039]    In a further development of the computer software product, the additional isolating mechanism is at least partly closed when the isolating mechanism is at least partly closed. In particular, the additional isolating mechanism is completely or substantially completely closed. when the isolating mechanism is completely or substantially completely closed. The more completely the additional isolating mechanism is closed, the more exhaust gas flows through the exhaust gas turbine, thereby increasing the rotating speed of the turbocompressor. In turn, the faster the turbocompressor rotates, the more intensely the combustion air is compressed. Since at the same time the isolating mechanism is at least partly closed, a portion of the combustion air flows through the compressor device and increases the speed thereof. Thus it is possible to influence the speed of the compressor device via the isolating mechanism and the additional isolating mechanism. 
         [0040]    In a further development of the computer software product, when the internal combustion engine is in coasting mode or the internal combustion engine is operated below or at its full suction load, the additional isolating mechanism is at least partly opened when the quantity of combustion air fed to the internal combustion engine exceeds a predetermined value or the predetermined value. As was described previously, it can happen during operation of the drive unit that the speed of the compressor device increases to such a level that there is a danger of damaging the compressor device. When the additional isolating mechanism is completely or partly opened, a portion of the exhaust gas flow passes through the waste gate line, and the rotating speed of the turbocompressor is reduced thereby. As a direct consequence of this, the combustion air is compressed less intensely, and for this reason the speed of the compressor device falls or does not even rise to a hazardous level. In addition, opening the additional isolating mechanism also serves to prevent the exhaust gas turbine and the turbocompressor from reaching a damaging level. 
         [0041]    A further embodiment of the present disclosure relates to a control unit and a control and/or regulating device with a computer software product according to any of the embodiments described previously. As with the computer software product, with the control unit and control and/or regulating device it is possible to control the drive unit in such a manner that fuel consumption is reduced and the response behavior of the internal combustion engine is improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]    The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements. 
           [0043]      FIG. 1  is a schematic diagram of a first embodiment of a drive unit; 
           [0044]      FIG. 2  is a schematic diagram of a second embodiment of the drive unit; 
           [0045]      FIG. 3  is a set of characteristic curves for an internal combustion engine to explain the computer program; and 
           [0046]      FIG. 4  is a flowchart illustrating a control mode with which the drive unit may be operated. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description. 
         [0048]      FIG. 1  shows schematic diagram representing a drive unit  10   1  according to a first embodiment for driving a motor vehicle (not shown). Drive unit  10   1  includes an internal combustion engine  12 , which supplied the necessary power for driving the motor vehicles, which may be for example a four-cylinder gasoline or Diesel engine. Internal combustion engine  12  typically functions according to the four-stroke principle, although a two-stroke principle is also conceivable here. Drive unit  10  includes a feeder line  16 , via which combustion air may be supplied to internal combustion engine  12 . A throttle valve  18  is arranged in feeder line  16 , and is movable between an open position, in which it is completely open, and a closed position, in which it is closed as far as possible, in the open position, internal combustion engine  12  may be operated with maximum load, whereas in the closed position internal combustion engine  12  may be operated in coasting mode. The exhaust gases that are generated by combustion of the mixture of combustion air and fuel are discharged by internal combustion engine  12  via a discharge line  20 . In order to draw the combustion air in from the surrounding atmosphere, internal combustion engine  12  may be equipped with an intake device  22 , which may include an air filter. Discharge line  20  is equipped with an exhaust gas treatment system  24 , which may include catalytic converters and filters, particularly particulate filters to filter and/or convert the toxic components contained in the exhaust gas into non-toxic compounds. The direction of flow of the combustion air and exhaust gases through feeder line  16  and discharge line  20  is indicated by arrows B. 
         [0049]    Drive unit  10   1  includes a compressor device  26  which cooperates with and compresses the combustion air in feeder line  16 . Compressor device  26  includes a compressor  36 , which in the example shown is driven via a driven shaft  38  of internal combustion engine  12  and is connectable optionally to internal combustion engine  12  or driven shaft  38  via a coupling device  40 . Compressor  36  has the form of a rotary compressor. Coupling device  40  may be realized as an electromagnetic coupling device  40 , for example. Drive unit  10   1  further includes a turbocharger device  28 , which is arranged upstream of compressor device  26  when viewed in the direction of flow of the combustion air to internal combustion engine  12 . Turbocharger device  28  includes a turbocompressor  30  arranged in feeder line  16  and an exhaust gas turbine  32  arranged in discharge line  20 , the two being connected to each other via a shaft  34 . 
         [0050]    Between turbocompressor  30  and compressor  36 , a bypass line  41  branches off from feeder line  16  and opens into feeder line  16  again downstream of compressor  36 . An isolating mechanism  42  is arranged in bypass line  41  and may be shifted between a completely open position and a completely closed position. In the example shown, isolating mechanism  42  includes a regulator valve  43 , which may be shifted steplessly between the open and closed positions. An air cooler  44  for cooling the combustion air that heats up under compression is arranged downstream of the point where bypass line  41  opens into feeder line  16  again. Air cooler  44  is often also called “intercooler”. 
         [0051]    A pressure sensor  45  is provided to determine the pressure in inlet manifold MAP. A control unit  46  is also present, and is connected to pressure sensor  45  via electrical wires  49  to receive the signals generated by pressure sensor  45 . Control unit  46  is also connected to throttle valve  18 , coupling device  40  and regulator valve  43 , also via electrical wires  49 . 
         [0052]    A “waste gate line”  47  is provided in discharge line  20 , providing the option to bypass the exhaust gas turbine  32  of turbocharger device  26 . Waste gate line  47  may be used to adjust the rotating speed of turbocharger device  26  and particularly to prevent turbocharger device  26  from over-rotating. For this purpose, waste gate line  47  includes a regulator valve  48 . 
         [0053]      FIG. 2  represents a second embodiment of drive unit  10   2 . This differs from the first embodiment solely in that compressor device  36  is not driven by internal combustion engine  12  but instead by a separate electric motor  50 . The electric motor  50  in this case is also connected to compressor  36  via a coupling device  40  and may be disconnected from it again. 
         [0054]    However, it should be noted at this point that if compressor device  36  is driven by electric motor  50  it is not essential to provide coupling device  40 . Accordingly, the disclosure is intended also to include an embodiment in which electric motor  50  is connected directly to compressor device  36 , and coupling device  40  may be entirely absent. 
         [0055]      FIG. 3  represents a set of characteristic curves for an internal combustion engine  12  that may be operated with the computer program. In this context, the torque M V  generated by internal combustion engine  12  as a function of the volume of its combustion chambers is plotted against the rotating speed of the internal combustion engine n vm  for a specific pressure in the intake manifold MAP (“manifold air pressure”), which is recorded by pressure sensor  45  (see also  FIGS. 1 and 2 ). The delivered volume-specific torque M V  represents a different way of expressing brake mean effective pressure BMEP. 
         [0056]    For the purposes of the present disclosure, the area of interest is the area in which the MAP is lower than atmospheric pressure, which is approximately 100 kPa. This area is located at or below the full suction load of the internal combustion engine. The set of characteristic curves is divided into a first zone  52  with a first lower limit  54  and a first upper limit  56  and a second zone  58  with a second lower limit  60  and a second upper limit  62 . The first upper limit  56  and the second lower limit  60  coincide. In the example shown, the first lower limit  54  is at 0 kPa, the first upper limit  56  and the second lower limit  60  are located at 70 kPa, and the second upper limit is located at 100 kPa, that is to say approximately atmospheric pressure. The graph of the first upper limit  56  and the second lower limit  60  in particular is determined by the characteristics and operating state of the internal combustion engine. As was stated in the introduction, a MAP lower limit of 0 kPa is only conceivable in theory, because this would mean that feeder line  16  housed a vacuum. An MAP lower than 10 kPa will only be recorded in exceptional situations in real life. During normal operation, the MAP will generally barely fall below 30 kPa. 
         [0057]    If pressure sensor  45  detects a MAP that is in first zone  52  or second zone  58 , drive unit  10  is operated in such a manner that compressor device  36  is disconnected from internal combustion engine  12  or from electric motor  50  by opening coupling device  40  following a corresponding command from control unit  46 , if this has not already taken place. 
         [0058]    If the MAP is in first zone  52 , so butterfly valve  43  in bypass line  41  is completely or partly closed and throttle valve  18  is completely or partly opened. Butterfly valve  43  and throttle valve  18  are also actuated by control unit  46 . The combustion air flows entirely through compressor  36  and drives it, thereby increasing its rotating speed without the need for internal combustion engine  12  or electric motor  50  to transfer any torque to compressor  32 . 
         [0059]    In second zone  58 , the MAP has already exceeded first upper limit  56  and second lower limit  60 , and this is recorded by pressure sensor  45 , In second zone  58 , the danger exists that the rotating speed of compressor device  26  will increase to a level at which damage may occur. In this case, throttle valve  18  is moved towards its closed position, and/or butterfly valve  43  is completely or partly opened. Both measures have the effect of reducing the quantity of combustion air that flows through compressor device  26 , so that the speed of compressor device  26  is reduced to a non-damaging level or kept below this level. 
         [0060]    If the MAP rises above 100 kPa, butterfly valve  43  is closed again and the load of internal combustion engine  12  cannot be changed except via throttle valve  18 . In addition, compressor device  26  is connected to internal combustion engine  12  or electric motor  50  by closing of coupling device  40 . Again, control unit  45  is tasked with initiating these steps. 
         [0061]    Internal combustion engine  12  is operated up to a maximum of full suction load both in first zone  52  and second zone  58 , whereas with a MAP of over 100 kPa the combustion air is compressed beyond atmospheric pressure and in this way the internal combustion engine is supplied by forced induction. 
         [0062]    If internal combustion engine  12  is in coasting or freewheeling mode, internal combustion engine  12  does not transfer any load. Instead, its pistons are moved by the motor vehicle&#39;s inertia, with the consequence that the volume-specific torque M V  assumes a negative value. This is the case in a third zone  64  of  FIG. 3 , which represents coasting mode. There is no fixed lower limit to the volume-specific torque M V  in the third zone  64 . Instead, it is determined by the mass and speed of the motor vehicles. If internal combustion engine  12  drives a heavy motor vehicle, and the vehicle is switched into coasting mode while travelling at high speed, volume-specific torque M V  takes on greater negative values than if the internal combustion engine  12  is switched to coasting mode in a light motor vehicle travelling at low speed. Coasting mode may be identified by sensors, for example, which calculated the speed of the motor vehicle and the position of the main coupling in the drivetrain of the motor vehicle and forward this information to control unit  46 . 
         [0063]    If internal combustion engine  12  is in coasting mode, compressor device  26  is decoupled from the internal combustion engine  12  or the electric motor  50  if this has not already taken place. Butterfly valve  43  is also completely or partly closed. If butterfly valve  43  is already closed, it will be kept closed. Throttle valve  18  is opened. All steps are initiated by control unit  45 . 
         [0064]    As was indicated in the introduction, in real life the MAP cannot fall below a certain value of about 10 to 30 kPa. In the example presented, the lowest measured value for MAP is 50 kPa. Once this lowest MAP has been reached, the MAP will not be affected any more by a falling volume-specific torque. In view of this, no further lines are shown in third zone  64  in the example illustrated. 
         [0065]      FIG. 4  is a flowchart representing the various steps that are performed by an embodiment of the computer program running on control unit  45  in order to operate drive unit  10 . First, it is determined whether the value delivered by internal combustion engine  12  for volume-specific torque M V &lt;0 Nm/L. This query is equivalent to the question as to whether internal combustion engine  12  is in coasting mode or not. This query does not necessarily have to be made on the basis of a measurement, it can be checked for example by determining whether internal combustion engine  12  is connected to the drivetrain via the main coupling, whether the motor vehicle is moving, and whether throttle valve  18  is closed. If these three questions are answered in the affirmative, internal combustion engine  12  is in coasting mode. However, the engine controller may provide that coasting mode is already assumed when throttle valve  18  is not fully closed. Further criteria may be used to determine whether the internal combustion engine is in coasting mode or not. 
         [0066]    If internal combustion engine  12  is in coasting mode, steps S 1  and S 2  are executed. In step S 1 , compressor device  36  is decoupled from internal combustion engine  12  or electric motor  50 . If this has already taken place, compressor device  36  will remain decoupled. In step S 2 , the second butterfly valve  43  will be completely or substantially closed, or kept closed, and throttle valve  18  will be fully or partly opened. 
         [0067]    If internal combustion engine  12  is not in coasting mode, a calculation is made to determine whether MAP&lt;100 kPa. To this end, pressure sensor  45  may be used. If this is the case, a further check is made to determine whether MAP&lt;MAP krit . With reference to  FIG. 3 , MAP krit  corresponds to the first upper limit  56  of first zone  52  and the second lower limit  60  of second zone  58  and is equal to 70 kPa. Other suitable values for MAP krit  may also be selected. If the MAP is lower than MAP krit , steps S 3 , S 4  and S 5  are executed. In step S 3 , compressor device  36  is decoupled from internal combustion engine  12  or electric motor  50  is this has not already taken place. In step S 4 , butterfly valve  43  is completely or partly closed, and in step S 5  the throttle valve is completely or partly opened. 
         [0068]    However, if the MAP is greater than MAP krit  but less than 100 kPa, steps S 6 , S 7  and S 8  are executed. In S 6  compressor device  36  is decoupled from internal combustion engine  12  or electric motor  50 , if this has not already taken place. In step S 7 , throttle valve  18  is moved towards its closed position, and in step S 8  the butterfly valve  43  is completely or partly opened. 
         [0069]    However, if the MAP is greater than 100 kPa, and therefore greater than atmospheric pressure, in step S 9  compressor device  36  is coupled to internal combustion engine  12  or electric motor  50  by closing the coupling device  40 . Regulator valve  43  can then be completely closed, although this is not absolutely necessary. The load on internal combustion engine  12  can then be modified with throttle valve  18 . 
         [0070]    While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist, It should also he appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.