Control device for controlling an internal combustion engine and method for heating an exhaust emission control device

An exhaust-gas purification system and method controls an internal combustion engine having at least one cylinder-piston unit operating in a overrun (drag) mode in which piston motion is induced by motion of an output shaft of a drive output unit associated with the internal combustion engine. A control device controls, for each of cylinder-piston unit, an intake fluid, an exhaust valve and fuel injection to heat an exhaust emission control device by deactivating fuel injection, passing the substantially fuel-free intake fluid into the cylinder, compressing and thereby heating the fluid in the cylinder, and passing the heated outlet fluid to the exhaust emission control device. The control device may control the amount of heating based on measurement and/or use of a temperature model of the exhaust emission control device.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a control device for controlling an internal combustion engine in an overrun mode, in order to keep an exhaust-gas purification device, arranged downstream of the internal combustion engine, at an operating temperature, or to bring said exhaust-gas purification device to said operating temperature, and to a method for heating an exhaust-gas purification device.

In order to satisfy the emission requirements for modern internal combustion engines, an exhaust-gas purification system is conventionally arranged downstream of an internal combustion engine and removes pollutants, for example NOX or soot, from the exhaust gas discharged by the internal combustion engine. Said exhaust-gas purification device has to have a minimum temperature for a functionally correct operation. During a normal operation of the internal combustion engine, said temperature is in principle provided, but if the internal combustion engine is kept in an overrun state for an extensive period of time, for example with extensive downhill driving or, in the case of a hybrid drive, with the use of an electric machine, the temperature of the exhaust-gas purification device can be reduced to such an extent, or be so low, that exhaust-gas purification is not possible. DE 19720381, for example, has therefore proposed that, during operation of an emission-free drive assembly, such as for example an electric machine, and prior to start-up of the internal combustion engine, the exhaust-gas purification device is brought to the required operating temperature by means of an additional heating element.

However, the disadvantage of this external and additional heating element is that it is necessary to apply additional electrical energy for the heating element and it is necessary to provide an installation space for the heating element.

It is therefore an object of the present invention to provide a possibility for keeping at, or for bringing to, an operating temperature an exhaust-gas purification device without provision having to be made of an additional heating system and without polluting the environment through excessive emissions of the exhaust gas.

Proposed below is a control device for controlling an internal combustion engine, having at least one cylinder-piston unit, in an overrun mode, which control device serves for bringing to an operating temperature, or for keeping at said operating temperature, an exhaust-gas purification device assigned to the internal combustion engine.

Here, by definition, in an overrun mode, a piston movement of the cylinder-piston unit is induced via a movement of a drive output unit assigned to the internal combustion engine, in particular a drive output shaft. Such an overrun mode can arise for example due to particular driving states, such as for example downhill driving or the removal of the foot from the gas pedal. Then, the piston is moved purely by the rotational movement transmitted from the wheels to the drive output shaft, if the internal combustion engine is coupled to the drive output shaft. Such an overrun mode can likewise be achieved if, for example in the case of purely electric driving, in which an electric machine transmits a torque to the wheels of the vehicle, the internal combustion engine is not decoupled from the electric machine by means of a clutch device, but rather remains coupled, with the result that the torque of the electric machine is transmitted not only to the wheels but also to the internal combustion engine. Here too, the movement of the piston is induced via the rotational movement of the drive output shaft.

Furthermore, each cylinder-piston unit of the internal combustion engine has an inlet valve in order to deliver an inlet fluid into the cylinder. According to the configuration of the engine, said inlet fluid may be pure air or an air-fuel mixture. The cylinder-piston unit furthermore has an outlet valve which transfers an outlet fluid into the exhaust-gas purification device. For a normal operation of the internal combustion engine, said outlet fluid is the exhaust gas, that is to say the combustion gases after the fuel combustion in the cylinder-piston unit has taken place. As mentioned above, by means of a fuel injection apparatus, fuel may be introduced directly into the inlet fluid upstream or downstream of the inlet valve. The control of the inlet valve and outlet valve and the fuel injection into the inlet fluid is controlled via the control device.

In order to make possible heating of the exhaust-gas purification device or maintenance of the exhaust-gas purification device at its operating temperature, it is proposed according to the invention that, in the overrun mode, the control device causes the means for fuel injection into the inlet fluid to be deactivated and activates the inlet and outlet valves such that the then substantially fuel-free inlet fluid, in other words the sucked-in air, is introduced into the cylinder, is compressed by the movement of the piston induced in the overrun mode, is heated by the compression, and, after the compression, is transferred as heated outlet fluid into the exhaust-gas purification device through the outlet valve.

As is known from the technology for diesel engines, the compression realized in the cylinder can result in the air being heated to several hundred degrees, and so an outlet fluid heated in this manner is perfectly capable of heating the exhaust-gas purification device arranged downstream to its operating temperature, or keeping said exhaust-gas purification device at its operating temperature.

The exhaust-gas purification device may for example be a three-way catalytic converter, a particle filter, a particle filter with a catalytic coating, a NOx storage catalytic converter, an SCR catalytic converter, an oxidation catalytic converter or a combination thereof. It goes without saying that exhaust-gas purification devices other than/in addition to the stated exhaust-gas purification devices may be present.

Here, this control device may be used firstly with pure internal combustion engines in the case of long downhill driving. However, what is particularly advantageous is the use with hybrid drives, in the case of which an emission-free drive, such as for example an electric machine, provides for the overrun mode of the vehicle. With such hybrid drives, there is always the problem that, prior to a connection of the internal combustion engine, the exhaust-gas purification device has to be brought to operating temperature so as to avoid an excessive emission of pollutants.

In order to determine whether a connection of the internal combustion engine in the hybrid drive will occur shortly, use may be made of a prediction model which is stored for example in a memory unit associated with the control device. Here, said prediction model predicts a connection of the internal combustion engine based for example on a driving profile, GPS data and/or traffic information data.

According to a further advantageous embodiment, the control device is furthermore designed to activate the outlet valve such that the outlet valve is opened when the piston is in a region of the top dead center. The fluid present in the cylinder, more precisely in the cylinder interior space, has its greatest compression, and thus its highest heating, in the region of the top dead center and, when it is discharged, can heat the exhaust-gas purification device effectively.

Here, however, the outlet valve may be opened in a position other than in the region of the top dead center. Although this can reduce the attainable temperature of the fluid in the cylinder, the attainable temperature is then also so high that heating of the exhaust-gas purification device is possible. Reasons for opening the outlet valve at other positions may be provided for example by hardware limitations.

It is furthermore advantageous for the control device to activate the outlet valve such that the outlet valve is opened when the heated outlet fluid has a desired or required temperature. It is thus possible for example for the outlet valve to be opened already prior to a maximum compression, it also however being possible to let the piston pass through multiple strokes until the fluid present in the cylinder has the corresponding temperature.

According to a further advantageous exemplary embodiment, it is also possible for use to be made of an exhaust-gas recirculation (EGR) system, in order to return already heated outlet fluid into an intake manifold of the internal combustion engine. Since already heated fluid is then introduced into the cylinder interior space, the temperature can once again be significantly increased. As an alternative or in addition to using an exhaust-gas recirculation system, it is also possible for the outlet valve to be activated such that, instead of, via activation of the inlet valve, fresh cold inlet fluid being introduced into the cylinder interior space, the outlet valve is opened during the intake, with the result that the heated outlet fluid is sucked back into the cylinder interior space and, there, can be heated further.

In order to determine the temperature of the heated outlet fluid, provision may be made in the cylinder of a measurement sensor which determines the temperature of the fluid.

Alternatively, however, it is also possible to merely estimate the temperature of the heated outlet fluid. For this purpose, it is possible, for example at an engine test stand, to measure, and to store in a temperature model, the change in temperature of the fluid present in the cylinder interior space during compression for several different scenarios. Said temperature model can then be stored in a memory device which interacts with the control device and be read out from said memory device, such that the control device opens the outlet valve whenever the temperature model defines that the heated fluid in the cylinder has a particular or desired temperature. Here, it is possible for a multiplicity of operating parameters of the internal combustion engine or of the drive system to be generally stored in the temperature model. In particular, the temperature model can furthermore determine a change in temperature based on the rotational speeds of the internal combustion engine, the temperatures of the inlet fluid, the ambient outside temperatures and/or the number of piston strokes. All of these parameters influence the temperature of the outlet fluid that is required for heating the exhaust-gas purification device, the heating rate which is attained with an outlet fluid at a particular temperature, and/or the temperature of the outlet fluid at a particular time. It goes without saying that, in addition to the stated parameters, consideration may be made of yet further parameters which have an influence on the temperature model.

According to a further advantageous embodiment, the control device is furthermore designed such that it allows reactivation of the means for fuel injection, and a transition of the valve activation into normal operation, only when the exhaust-gas purification device has attained a particular minimum temperature, in particular the operating temperature thereof. This ensures that “normal” internal combustion engine operation or a connection of the internal combustion engine is realized only when effective exhaust-gas purification is ensured. The attainment of the operating temperature may likewise be measured by a measurement sensor.

Alternatively or additionally, however, it is also possible for the attainment of the corresponding operating temperature of the exhaust-gas purification device to be estimated, in that the temperature profiles are determined at a test stand for a wide variety of operating parameters and stored in the temperature model. This makes it possible for the temperature model also to define when and under what conditions the exhaust-gas purification device attains its operating temperature.

Furthermore, account can be taken of aging-induced increases in operating temperature of the exhaust-gas purification device by both the measurement sensors and the temperature model. This is advantageous in particular since, in a manner dependent on the mileage or generally an aging state of the exhaust-gas purification device, the minimum operating temperature of the latter is increased over the course of time.

The use of the temperature model has the advantage that provision does not have to be made in the cylinder or the exhaust-gas purification device of additional units, such as for example temperature measurement sensors, which interact with the control device.

Since the temperature model maps the temperature profiles of the fluid in the cylinder or of the heated outlet fluid and/or of the exhaust-gas purification device for a wide variety of operating states, it is generally possible for highly reliable statements concerning an attained temperature state of both the fluid and the exhaust-gas purification device to be made.

It is likewise advantageous if the control device does not automatically activate, according to the above description, the means for fuel injection or the valves for each detected overrun mode, but rather checks beforehand whether heating of the exhaust-gas purification device is necessary at all. Such heating may be necessary for example if, by means of the aforementioned prediction model, a connection of the internal combustion engine is pending and/or if the temperature of the exhaust-gas purification device is below the operating temperature. Whether the latter is case can be determined via direct measurement using the measurement sensor or via the aforementioned temperature model.

According to a further advantageous embodiment, it goes without saying that, as before, an additional heating element, such as for example a heatable plate, an electrical catalytic converter or the like, may be present upstream of the exhaust-gas purification device.

A further aspect of the present invention relates to a hybrid drive system of a hybrid vehicle, having an electric machine and having an internal combustion engine, wherein the internal combustion engine is activated as described above by a control device.

A further aspect of the present invention relates to a method for activating an internal combustion engine, in particular an internal combustion engine in a hybrid drivetrain of a hybrid vehicle as described above, wherein the method has the steps:overrunning the internal combustion engine for a movement of the piston induced by the electric machine and/or by a driving state;deactivating a means for fuel injection in the inlet fluid;introducing a substantially fuel-free inlet fluid into the cylinder;compressing and thus heating the fluid in the cylinder by way of the induced movement of the piston, and thus providing a heated outlet fluid;discharging the heated outlet fluid into the exhaust-gas purification device; andheating the exhaust-gas purification device by means of the heated outlet fluid.

Here, it is advantageous in particular if, prior to the method being carried out, by means of the temperature model or an internal combustion engine start prediction model, a check is made as to whether heating of the exhaust-gas purification device is necessary.

It is furthermore preferable if the method has one of the following steps:providing, by way of measurement at an engine test stand, a temperature model for the heating of the fluid present in the cylinder in the overrun mode;storing the temperature model in a memory apparatus in the vehicle;reading out the temperature model from the memory apparatus;opening the outlet valve, and discharging the heated outlet fluid, when the temperature model defines that the fluid in the cylinder has a particular temperature.

Additionally, the method may advantageously have the one of the following steps:providing in the temperature model, by way of measurement at the engine test stand, a temperature change profile of the exhaust-gas purification device, which is based on at least the temperature of the heated outlet fluid;reactivating the means for fuel injection, and activating the inlet and outlet valves according to a normal operation for the internal combustion engine, when the temperature model defines that the exhaust-gas purification device has attained an operating temperature.

The embodiments and features described for the proposed control device accordingly apply to the proposed method.

Also proposed is a computer program product having program code which is configured to initiate the carrying-out of the aforementioned method on a processor of the control unit.

A computer program product, such as for example a computer program medium, may be provided or supplied as a storage medium, such as for example a memory card, USB stick, CD-ROM, DVD or else in the form of a downloadable file from a server in a network. This may be realized for example in a wireless communication network by the transmission of a corresponding file with the computer program product or the computer program medium.

Further possible implementations of the invention also comprise not explicitly stated combinations of features or embodiments that are described above or below and with respect to the example embodiments. Here, a person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

Further advantages and advantageous embodiments are specified in the description, the drawings and the claims. Here, the combinations of the features that are specified in the description and in the drawings are in particular purely examples, and so the features may also be provided individually or so as to be differently combined.

Below, identical elements or elements of functionally identical action are denoted by the same reference signs.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1shows two different configurations of a hybrid drive system1, wherein, inFIG. 1A, an internal combustion engine2is connected via a transmission4and a clutch device6to a drive output unit8, in particular vehicle wheels10, while an electric machine12is connected to another pair of vehicle wheels14. This means that the vehicle constructed in this manner is driven by the internal combustion engine2at one wheel axle16, while it is driven by an electric machine12at the other wheel axle18. Here, the electric machine12and the internal combustion engine2can jointly provide for a drive of the vehicle1, it also however being possible for only the electric machine12or the internal combustion engine2to drive the vehicle.

FIG. 1Bshows an alternative configuration of a vehicle having a hybrid drive, in which only one vehicle axle16is driven, while the other vehicle axle18merely co-rotates. In this case, the internal combustion engine2and the electric motor12are able to be connected to one another, or disconnected from one another, via the clutch unit6. Also in this case, it is thereby possible for a combined operation of the internal combustion engine2and the electric motor12, or a disconnected operation of only the electric motor12or only the internal combustion engine2, to be provided. It goes without saying that other configurations are also possible.

As is conventional, the internal combustion engine2has multiple cylinder-piston units20, of which one is schematically shown inFIG. 2. The cylinder-piston unit20or the internal combustion engine2is furthermore, asFIG. 2shows, connected to an exhaust-gas purification device30. Such an exhaust-gas purification device, also referred to as a catalytic converter, purifies the exhaust gases of the internal combustion engine2of pollutants, such as for example nitrogen oxides or soot. For an effective exhaust-gas purification, however, the exhaust-gas purification device30must have a particular operating temperature. This can, moreover, change with increasing age of the exhaust-gas purification device30.

In the case of an overrun mode of the internal combustion engine2, for example during downhill driving or for a purely electrical drive, a situation may however arise in which the operating temperature of the exhaust-gas purification device30can no longer be maintained. Likewise, in the case of hybrid drives, as shown inFIG. 1, it may be the case that, if the internal combustion engine2is to be connected to the electric motor12after purely electric driving, the temperature of the exhaust-gas purification device30is not at operating temperature, and so, in both cases, effective exhaust-gas purification cannot be carried out.

As mentioned,FIG. 2schematically shows a cylinder-piston unit20of an internal combustion engine2, wherein the cylinder-piston unit20has a cylinder22and piston24which is movable therein, wherein the piston24is in turn connected to a drive output unit8, in particular a transmission input shaft26, in order to transmit a torque to the wheels10. The cylinder-piston unit20furthermore has an inlet valve32, an outlet valve34and a fuel injection apparatus36, which, broadly in principle, interact with one another such that air is introduced via the inlet valve32from an intake manifold38into the cylinder interior space28, has fuel added to it there by the fuel injection apparatus36and is then ignited, and the exhaust gas forming during the combustion is transferred via the outlet valve36to the exhaust-gas purification device30. With this normal operation, the movement of the piston24is induced via the combustion taking place in the interior space28of the cylinder-piston unit20and the accompanying expansion and pressure movement of the piston24downward. During the aforementioned overrun mode, however, the movement of the piston24is induced via, for example, the rotational movement of the wheels10or via the torque transmission of the electric machine12.

Here, the inventor has recognized that this induced movement of the piston24may be used to compress a fluid in the cylinder space28, and in this way to heat said fluid, and to deliver the heated fluid to the exhaust-gas purification device30in order to heat the latter.

In order to make possible such heating of the exhaust-gas purification device30, a control device40which activates both the inlet valve32and the outlet valve34and the fuel injection apparatus36is furthermore proposed. The inlet valve32, the outlet valve34and the fuel injection apparatus36are conventional elements of the internal combustion engine2and, as mentioned above, are conventionally activated by the control device40such that the inlet fluid42(for example air) is introduced via the inlet valve32into the working space28of the cylinder-piston unit20. In this case, the inlet fluid42may be an air-fuel mixture, wherein then the fuel injection apparatus36is arranged upstream of the valve34, or, as in the case illustrated inFIG. 2, pure sucked-in air which is introduced into the interior space28of the cylinder-piston unit20and has fuel added to it there. After ignition of the air-fuel mixture has taken place in the piston cylinder interior space28, the exhaust gas44which thus forms is transferred via the outlet valve34into the exhaust-gas purification system30.

If the exhaust-gas purification system30is then to be heated, however, for example because the temperature Tcatof the exhaust-gas purification device30is below its operating temperature Tcat,targor because a start-up of the internal combustion engine2is likely, the control unit40controls the inlet valve32, the outlet valve34and the fuel injection apparatus36such that the fuel injection is deactivated, and a substantially fuel-free inlet fluid42is introduced via the inlet valve32into the interior space28of the cylinder-piston unit20. There, said fluid is compressed by the movement of the piston24induced by the overrun mode and is heated during this compression, with the result that the resulting heated fluid is transferred as heated outlet fluid44into the exhaust-gas purification device30through the outlet valve34. Since, during said compression, temperatures of several hundred degrees Celsius can be easily attained, heating of the exhaust-gas purification device30is possible without any problems. Here, it is in particular preferable if the outlet valve34is activated by the control device40such that it is opened when the piston24is in a region of the top dead center, that is to say the fluid is in a state of high compression.

Alternatively or additionally, the control device40can control the outlet valve34such that the outlet valve34is opened when the fluid in the cylinder interior space28has attained a particular temperature TF. Said temperature TFmay be determined for example via a temperature sensor46arranged in the cylinder interior space.

Furthermore, the control device40may be designed to allow an injection of fuel and a normal operation of the inlet and outlet valves32,34only when a temperature of the exhaust-gas purification system Tcathas attained a particular value. This temperature may also be measured for example via a temperature sensor48present in the exhaust-gas purification device30, and be made available to the control device40.

Instead of the direct measurement of the temperatures in the cylinder interior space28or in the exhaust-gas purification system30, it is also possible for the control device40to be assigned a memory module50, for example integrated in the control device40, in which memory module a temperature model of the fluid temperature TF, and/or of the exhaust-gas purification device temperature Tcat, is stored. Here, the temperature model can be determined for example via measurements at an engine test stand, with which the temperature profiles of the temperatures TFand Tcatare measured for different operating parameters and engine settings. Here, the temperature model may for example be a multi-dimensional matrix which contains for example information about the temperature of the inlet fluid, the temperature of the surroundings, the rotational speed of the overrun engine, the volumetric flow rate of the outlet fluid, the temperature of the outlet fluid and the temperature of the exhaust-gas purification system. It goes without saying that further information about relevant operating parameters may be contained in the matrix. In the control unit50, it is furthermore also possible to store a prediction model which, for example on the basis of GPS data and/or traffic information, predicts a connection of the internal combustion engine and thus the requirement for an exhaust-gas purification device at operating temperature.

On the basis of said multi-dimensional parameters, the control device40can establish for example when, at a given temperature of the inlet fluid TeF, at a given temperature of the outlet fluid TF, at a given volumetric flow rate of the outlet fluid VFand/or at a given engine rotational speed n, an operating temperature Tcat,targof the exhaust-gas purification device is attained.

Schematically, such a relationship can be illustrated for example via a diagram, as shown inFIG. 3. The diagram shown inFIG. 3is a time-temperature diagram, with the temperature of the catalytic converter Tcatbeing plotted over time t. By way of example,FIG. 3indicates two temperature profiles I, II which are obtained for example for different starting parameters. It can be seen here that, with the temperature profile I, the exhaust-gas purification device30is at its operating temperature Tcat,targquicker than in the case in which the parameters of the graph II are used.

Here, the increase in temperature of the catalytic converter Tcatin principle significantly dependent on the temperature of the outlet fluid TF. The temperature of said outlet fluid TFmay be in turn influenced for example via the strength of the compression or the temperature of the inlet fluid. Here, it is also possible for use to be made of an exhaust-gas recirculation system52(seeFIG. 2) to use already compressed and heated air as an inlet fluid such that the heated air is compressed once again and the temperature thereof thus further increased. Another important parameter for increasing the temperature of the catalytic converter is the frequency at which the catalytic converter is provided with the heated air. This may be regulated for example via the rotational speed of the engine. Instead of using an exhaust-gas recirculation system for the recirculation of compressed heated air, the air may also be kept in the cylinder interior space for multiple piston strokes.

Overall, it is possible by way of the proposed control device or the proposed method for an exhaust-gas purification device to be kept at an operating temperature, or to be brought to the operating temperature, during an overrun mode of the internal combustion engine without provision having to be made of an additional heating device. This makes it possible for cost-saving and energy-saving heating of the exhaust-gas purification device to be provided.

REFERENCE SIGNS