Method and device for regenerating a particulate filter in a motor vehicle with a hybrid drive

Abstract

The invention relates to a method for regenerating a particulate filter in the exhaust gas channel of a motor vehicle with a hybrid drive consisting of an electric motor and an internal combustion engine. In this context, the internal combustion engine is lugged by the electric motor in order to regenerate the particulate filter. The internal combustion engine transports oxygen-rich air into the exhaust gas channel, a process in which the soot retained in the particulate filter is oxidized by the oxygen and the particulate filter can thus be regenerated. In this process, during the regeneration of the particulate filter, the quantity of air is controlled by a throttle valve in the air supply means of the internal combustion engine in order to allow the particulate filter to be regenerated as quickly and efficiently as possible. The invention also relates to a motor vehicle with a hybrid drive comprising an internal combustion engine and an electric motor, whereby the hybrid drive has a control unit to carry out such a method for the regeneration of the particulate filter.

Claims

1. A method for regenerating a particulate filter in an exhaust gas channel of a motor vehicle with a hybrid drive consisting of an electric motor and an internal combustion engine, whereby the particulate filter is arranged in the exhaust gas channel of the internal combustion engine, and whereby the internal combustion engine is connected to an air supply means comprising a throttle valve, said method comprising the following steps: operating the motor vehicle in the hybrid mode of operation, whereby the exhaust gas of the internal combustion engine is transported through the particulate filter during the operation of the internal combustion engine, ascertaining the load state of the particulate filter, initiating the regeneration of the particulate filter once the load state of the particulate filter has reached a defined maximum load state, carrying out a regeneration process of the particulate filter, whereby the internal combustion engine and the electric motor are coupled during the regeneration and the electric motor lugs the internal combustion engine, whereby transporting air, by the internal combustion engine, into the exhaust gas channel in order to oxidize the soot particles retained in the particulate filter, and controlling the throttle valve of the air supply means of the internal combustion engine during the regeneration of the particulate filter, irrespective of any torque demand the driver makes of the hybrid drive, while the internal combustion engine is dragged by the electric motor and fuel supply to the internal combustion engine is switched off, wherein the method is carried out in an externally ignited internal combustion engine, and wherein the throttle valve is closed at the end of the regeneration of the particulate filter.

2. The method according to claim 1, wherein the throttle valve is placed in a defined position at the beginning of the regeneration of the particulate filter.

3. The method according to claim 2, wherein the opening angle of the throttle valve at the beginning of the regeneration yields a markedly unthrottled operating point.

4. The method according to claim 3, wherein the opening angle of the throttle valve at the beginning of the regeneration is between 30° and 70°.

5. The method according to claim 1, wherein the opening angle of the throttle valve is continuously and steadily reduced from the beginning of the regeneration to the end of the regeneration.

6. The method according to claim 5, wherein the reduction of the opening angle of the throttle valve during the regeneration of the particulate filter takes place as a function of the temperature and/or the soot load of the particulate filter.

7. The method according to claim 1, characterized in that wherein the regeneration process is preceded by a heating process in which the particulate filter is heated up to the temperature range needed for the oxidation of the soot.

8. The method according to claim 7, wherein the internal combustion engine is operated at a stoichiometric air-fuel ratio during the heating phase.

9. The method according to claim 7, wherein the load point of the internal combustion engine is shifted during the heating phase in such a way that the internal combustion engine has to deliver an additional load to counter the work of the electric motor due to the battery being charged.

10. The method according to claim 1, wherein the throttle valve is closed and the internal combustion engine is started, even if the regeneration of the particulate filter is not yet complete, when the load demand made of the hybrid drive exceeds a certain threshold value.

11. The method according to claim 1, wherein the load point of the electric motor is shifted during the regeneration of the particulate filter in such a way that exclusively the electric motor delivers the torque required by the driver for the motor vehicle and additionally lugs the internal combustion engine.

12. The method according to claim 11, wherein the regeneration of the particulate filter takes place in a torque-neutral manner when it comes to the propulsive drive torque of the motor vehicle.

13. A control unit for a motor vehicle with a hybrid drive consisting of an internal combustion engine and an electric motor, said control unit being configured to carry out a method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in greater detail below in embodiments making reference to the accompanying drawings. The following is shown:

(2) FIG. 1: a first embodiment of a motor vehicle according to the invention, with a hybrid drive consisting of an internal combustion engine and an electric motor;

(3) FIG. 2: another embodiment of a motor vehicle according to the invention, with a hybrid drive;

(4) FIG. 3: a first flow diagram of a method according to the invention for the regeneration of a particulate filter in a motor vehicle with a hybrid drive; and

(5) FIG. 4 another flow diagram of a method according to the invention for the regeneration of a particulate filter in a motor vehicle with a hybrid drive.

BRIEF DESCRIPTION OF THE DRAWINGS

(6) FIG. 1 shows a schematic view of a motor vehicle 1 with a hybrid drive 2. The hybrid drive 2 comprises an internal combustion engine 10 and an electric motor 20, both of which can be operatively connected to a shared transmission 46 via a gear train 26. The internal combustion engine 10 is connected on the inlet side to an air supply means 30. In this context, as seen in the flow direction of the fresh air, the air supply means 30 has an air filter 32, an air mass meter 38 downstream from the air filter 32, and further downstream a compressor 36 of a turbocharger 40 and a throttle valve 34. The internal combustion engine 10 is connected on the outlet side to an exhaust gas channel 12 in which there is a turbine 18 in the flow direction of the exhaust gas, said turbine being connected to the compressor 36 of the turbocharger 40 via a shaft. Downstream from the turbine 18, there is a catalytic converter 14, and further downstream a particulate filter 16. The transmission 46 can be connected to the internal combustion engine 10 via a first coupling 48 and to the electric motor 20 via a second coupling 50. Here, the internal combustion engine 10 and the electric motor 20 can each propel the motor vehicle 1, either individually or jointly. For this purpose, the internal combustion engine 10 is connected via the transmission 46 to a first drive axle of the motor vehicle 1, and the electric motor 20 is connected to a second drive axle 44 of the motor vehicle 1. The electric motor 20 is connected to a battery 22 that supplies the electric motor 20 with electric power. The electric motor 20 and the internal combustion engine are connected via signal lines 28 to a control unit 24 of the hybrid drive 2 that transmits the power demands of the driver to the two drive aggregates 10, 20. As an alternative, the hybrid drive 2 can also be configured with a naturally aspirated engine, whereby in this case, the turbocharger 40 with the compressor 36 and the turbine 18 have been eliminated.

(7) FIG. 2 shows another embodiment of a motor vehicle 1 according to the invention, with a hybrid drive 2. In this context, the internal combustion engine 10 and the electric motor 20 are preferably arranged crosswise to the driving direction of the motor vehicle 1 in an engine compartment located at the front of the motor vehicle. As an alternative, the internal combustion engine 10 and the electric motor 20 can also be arranged along the driving direction. Between the internal combustion engine 10 and the transmission 46, there is a first coupling 48 via which the internal combustion engine 10 can be mechanically connected to the transmission 46. The first coupling 48 can be configured either as a simple shifting clutch or else as a preferably automatic dual clutch. Between the transmission 46 and the electric motor 20, there is another coupling 50 that allows the electric motor 20 to be coupled and uncoupled.

(8) A tank for the internal combustion engine 10 and a battery 22 for the electric motor 20 are arranged in the rear of the vehicle in order to achieve a uniform weight distribution between the first drive axle 42, preferably the front axle of the motor vehicle 1, and the second axle, preferably the rear axle. As an alternative, the tank and/or the battery 22 can also be arranged in other places in the motor vehicle 1.

(9) The internal combustion engine 10 has an air supply means 30 in which, as seen in the flow direction of the fresh air, there is an air filter 32 as well as an air mass meter 38 downstream from the air filter 32. As an alternative, the air mass meter 38, especially a hot-film air mass meter, can also be integrated into the air filter 32. Downstream from the air mass meter 38, there is a throttle valve 34 that can regulate the air feed into the combustion chambers of the internal combustion engine 10.

(10) The electric motor 20 and the internal combustion engine 10 can be connected to each other via a shared drive train 26, whereby they can be connected and disconnected by means of the couplings 48 and 50. When only one of the couplings 48 or 50 is closed, a selection can be made to operate the motor vehicle 1 either exclusively electrically by means of the electric motor 20 or else exclusively by means of the internal combustion engine 10. If both couplings 48 and 50 are closed, both drive aggregates 10, 20 can carry out a boost operation, a recuperation, in other words, charging of the battery 22 of the electric motor 20, or else an electric braking operation. The transmission 46 is connected to a differential that propels the wheels of the first drive axle 42, especially the front axle, via drive shafts.

(11) The internal combustion engine 10 has an exhaust gas channel 12 in which a three-way catalytic converter 14 and a particulate filter 16 are installed. A control unit 24 is provided to control the internal combustion engine 10 and the electric motor 20, said control unit 24 being connected to the internal combustion engine 10 via first signal lines 28, and to the electric motor 20 via second signal lines 28.

(12) During normal operation, the motor vehicle 1 is operated in a hybrid mode of operation in which the torque that the driver has requested from a given drive aggregate 10, 20 is transmitted by the control unit 24 to the internal combustion engine 10, to the electric motor 20, or to both drive aggregates 10, 20. The operating strategy of the hybrid drive 2 stored in the control unit 24 prescribes the way in which the driver request will be met. In this process, the drive torque is provided either completely by the electric motor 20, or by distributing the drive torque between the electric motor 20 and the internal combustion engine 10, or else completely by the internal combustion engine 10. In the hybrid mode of operation, it is also possible for the internal combustion engine 10 to generate more torque than is necessary to propel the motor vehicle, whereby the extra torque brought about by coupling the electric motor 20 via the coupling 50 is used in order to charge the battery 22 of the electric motor 20.

(13) While the internal combustion engine 10 is active, the exhaust gas of the internal combustion engine is transported through the particulate filter 16 in the exhaust gas channel 12. During the hybrid mode of operation, the particulate filter 16 is loaded with soot particles until a maximally permissible load state of the particulate filter 16 is reached.

(14) FIG. 3 shows a flow chart for the regeneration of the particulate filter 16. In a first phase I, the motor vehicle is operated in a hybrid mode of operation I until the particulate filter 16 reaches a maximally permissible load state. In this process, the opening angle α of the throttle valve 34 can be varied between 0% and 100%, and it depends on the power demand being made of the internal combustion engine 10. The maximally permissible load state can be determined by means of a differential pressure measurement via the particulate filter 16 or else by means of a modeling of the soot that enters into and exits from the particulate filter 16 employing a calculation model stored in the control unit 24. If it is ascertained that there is a need for the particulate filter 16 to be regenerated, then, in a second phase II, the particulate filter 16 is heated up to the temperature needed for the regeneration. The heating phase II of the particulate filter 16 is followed by the regeneration phase III of the particulate filter 16. The regeneration phase III of the particulate filter 16 can be carried out in several steps III1 to III5 as shown in FIG. 4, or else continuously as shown in FIG. 3. FIG. 4 shows a regeneration involving five regeneration steps, but regenerations with more or fewer regeneration steps are likewise possible. Moreover, the heating phase II can be dispensed with if the particulate filter 16 is already at the temperature needed to oxidize the soot that had been retained in the particulate filter 16 when the regeneration phase III was initiated. During the heating phase II, the internal combustion engine 10 is operated under load until an upper threshold temperature TSO has been reached. This upper threshold temperature is, for instance, 750° C., as a result of which ideal conditions are created for the oxidation of the soot retained in the particulate filter 16. The heating phase II can involve, for example, a shift of the ignition point in the late direction and/or an additional loading of the internal combustion engine 10 through a generator operation of the electric motor 20. In this context, the internal combustion engine 10 is preferably operated at a stoichiometric air-fuel ratio. Once the upper threshold temperature T.sub.SO has been reached, the injection of fuel into the combustion chambers of the internal combustion engine 10 is stopped and the internal combustion engine 10 is lugged by the electric motor 20. During this regeneration phase III, the internal combustion engine 10 is turned by the electric motor 20, a process in which the internal combustion engine 10 transports air into the exhaust gas channel 12. During the regeneration phase III, which constitutes an overrun phase of the internal combustion engine 10, the soot in the particulate filter 16 is oxidized, whereby the exhaust gas temperature drops due to the absence of burning in the combustion chambers of the internal combustion engine 10. Here, as an alternative, the injection of fuel into individual cylinders or into all of the cylinders of the internal combustion engine 10 can be discontinued. During the regeneration phase III, the internal combustion engine 10 does not deliver any drive torque, so that the entire drive torque has to be generated by the electric motor 20. Here, the opening angle α of the throttle valve 34 is set at a fixed value, for example, 50%, at the beginning of the regeneration of the particulate filter 16, and the throttle valve 34 is continuously closed during the regeneration of the particulate filter 16 until an opening angle α of the throttle valve 34 of 0%, that is to say, a maximum throttling of the quantity of fresh air, is reached at the end of the regeneration. The regeneration phase III is maintained until the temperature at the particulate filter 16 has reached a lower threshold value T.sub.SU of approximately 600° C. No further oxidation of the soot is possible below this temperature, so that a heating phase II has to be initiated once again. For the regeneration of the particulate filter 16, it is possible to alternate between heating phase II and regeneration phase III. This alternation between heating phase II and regeneration phase III is continuously repeated until the particulate filter 16 can be considered to have been regenerated, which can be done by means of a differential pressure measurement via the particulate filter 16 or else by means of modeling of the load state via a calculation model. Closing the throttle valve 34 at the end of the regeneration III creates a negative pressure in the intake duct of the internal combustion engine 10, thus allowing a very gentle re-start of the combustion in the combustion chambers of the internal combustion engine 10.

(15) After the regeneration of the particulate filter 16 has been successfully completed, the motor vehicle is once again operated in a hybrid mode of operation I and the particulate filter 16 is once again loaded with soot particles.

(16) FIG. 4 shows another diagram for the regeneration of the particulate filter 16. In a sequence that is essentially the same as that described in FIG. 3, the throttle valve 34 is closed here in discrete increments by, for example, 10% per increment. In this process, at the beginning of the regeneration III.sub.1 of the particulate filter 16, the throttle valve 34 is opened by a defined, fixed opening angle α of, for instance, 60%, whereby with every further step III.sub.2 to III.sub.5, the throttle valve 34 is closed further by a defined amount until, by the completion of the regeneration of the particulate filter 16, the throttle valve 34 is at least essentially closed and has a maximal residual opening of 10%.

(17) If a load demand that exceeds the output of the electric motor 20 is made of the hybrid drive 2 during the regeneration of the particulate filter 16, then the throttle valve 34 is closed in order to facilitate the start-up of the internal combustion engine 10. The regeneration phase III of the particulate filter 16 is interrupted in this process until appropriate conditions for a regeneration of the particulate filter 16 are once again present.

(18) The method according to the invention creates a very efficient mechanism for burning off soot particles on the particulate filter 16. Owing to the lugging operation of the internal combustion engine 10 by the electric motor 20, the inflow of oxygen into the exhaust gas channel 12 can be regulated largely independently of the load point of the hybrid drive 2. The torque needed to lug the internal combustion engine 10 is generated by the electric motor 20, so that the regeneration of the particulate filter 16 is imperceptible to the driver of the motor vehicle 1 and also very comfortable.

(19) In order to optimize the regeneration, as described above, the load point of the internal combustion engine 10 (especially during the heating phase II) as well as the load point of the electric motor 20 can be shifted during the overrun phase. In this process, the internal combustion engine 10 is uncoupled from the drive train of the motor vehicle 1 with the hybrid drive 2 during the regeneration. This yields a very simple regeneration possibility for the particulate filter 16.

LIST OF REFERENCE NUMERALS

(20) 1 motor vehicle 2 hybrid drive 10 internal combustion engine 12 exhaust gas channel 14 catalytic converter 16 particulate filter 18 turbine 20 electric motor 22 battery 24 control unit 26 drive train 28 signal line 30 air supply means 32 air filter 34 throttle valve 36 compressor 38 air mass meter 40 turbocharger 42 first drive axle 44 second drive axle 46 transmission 48 first coupling 50 second coupling S soot load of the particulate filter P progress of the particulate filter regeneration t time α opening angle of the throttle valve α.sub.FIX opening angle during the regeneration as prescribed by the method I hybrid drive II heating phase of the particulate filter III regeneration phase of the particulate filter III.sub.1 first step of the regeneration III.sub.2 second step of the regeneration III.sub.3 third step of the regeneration III.sub.4 fourth step of the regeneration III.sub.5 fifth step of the regeneration