Abstract:
A method is introduced for heating an exhaust-gas aftertreatment system ( 15 ). The method has the following steps: detection of a necessity to heat (S 1 ) the exhaust-gas aftertreatment system ( 15 ), and actuation (S 5 ) of an electric motor ( 5 ) in such a way that the electric motor ( 5 ) drags the internal combustion engine ( 3 ) which produces exhaust gas. Here, the internal combustion engine ( 3 ) is held at a predefinable rotational speed by the electric motor ( 5 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Exhaust gas reduction and monitoring are important issues of modern branches of industry. The exhaust gases of an internal combustion engine must be treated in exhaust gas aftertreatment systems for reasons of emission regulations among other reasons. A certain working temperature is necessary for the optimal functionality of an exhaust gas aftertreatment system. 
         [0002]    The exhaust gas aftertreatment system is heated with the aid of the exhaust gases generated in the internal combustion engine in order to achieve or to maintain the desired working temperature. Here a large proportion of the energy of combustion in the internal combustion engine is used for torque generation by the engine. A smaller proportion of the energy is output in the form of heat or of thermal energy. 
         [0003]    In order to achieve the emission targets, during a cold start the catalyzer must be brought to working temperature as rapidly as possible. One option for this is by retarding the ignition angle. This reduces the proportion of the energy for torque generation and at the same time increases the thermal portion. The proportion of the energy that can be given off as heat to the exhaust gas aftertreatment system together with the exhaust gases cannot be increased without restriction. It is limited by the internal combustion engine not being able to compensate for its losses and thus running roughly or even cutting out, if the torque-generating portion of the energy is reduced excessively. 
       SUMMARY OF THE INVENTION 
       [0004]    There can thus be a need for an improvement and/or acceleration of the heating of an exhaust gas aftertreatment system. 
         [0005]    Such a requirement can be satisfied by the subject of the present invention according to the independent claims. Advantageous embodiments of the present invention are disclosed in the dependent claims. Features, details and possible advantages of embodiments of the invention are discussed in detail below. 
         [0006]    According to a first aspect of the invention, a method for heating an exhaust gas aftertreatment system is proposed. The method comprises the following steps: detecting a need to heat the exhaust gas aftertreatment system; and controlling an electric motor such that the electric motor drags the internal combustion engine generating the exhaust gas. The internal combustion engine is thereby maintained at a specifiable revolution rate by the electric motor. 
         [0007]    In other words, the idea of the invention is based on operating the internal combustion engine regardless of how the engine is running such that a high exhaust gas temperature exists. A regular revolution rate profile of the internal combustion engine is thereby guaranteed by the electric motor. 
         [0008]    For example, for this purpose an ignition time can be selected to be so late that a piston has moved far towards bottom dead center before the fuel-air mixture in the combustion chamber of the cylinder is fully burnt. This causes an increase in the thermal energy released during combustion. But the torque or the power of the engine decreases here at the same time. During operation without an electric motor this could cause the internal combustion engine to run “roughly” or to cut out. However, according to the invention the internal combustion engine is dragged by the electric motor and is thus maintained at a specifiable, e.g. a constant, revolution rate. The revolution rate can be adjusted here, for example automatically by a control device of a vehicle or by a driver of the vehicle. 
         [0009]    The method can e.g. be used in hybrid vehicles with internal combustion engines and electric motors. 
         [0010]    The exhaust gas aftertreatment system can comprise a plurality of components, such as e.g. a catalyzer and a particle filter. A lambda probe can also be provided in, on or before the exhaust gas aftertreatment system. With the aid of the method according to the invention, individual components, such as a catalyzer and lambda probe, or the entire exhaust gas aftertreatment system can be heated. 
         [0011]    For detecting a need to heat the exhaust gas aftertreatment system, e.g. a probe or a sensor can be provided, which for example can recognize or measure a cold start of the internal combustion engine. A temperature sensor can also be provided directly in the exhaust gas aftertreatment system. 
         [0012]    The control of the electric motor can include regulation or readjustment of the revolution rate of the electric motor. The electric motor can drag the internal combustion engine irrespective of the torque of the internal combustion engine. The specifiable revolution rate at which the internal combustion engine is maintained by the electric motor can, for example, be constant or e.g. varied by a control device or a driver of a vehicle. 
         [0013]    The method according to the invention has the advantage that the time until achieving an optimal working temperature of the exhaust gas aftertreatment system, also referred to as the “Light-Off” time, can be reduced following a cold start of an internal combustion engine for example. Through the boosted and accelerated heating of the exhaust gas aftertreatment system with exhaust gases of the internal combustion engine, in particular the necessary working temperature can be achieved faster at a catalyzer and a lambda probe. This causes a reduction of emissions. When using said method in hybrid vehicles the internal combustion engine can also be shut off earlier, which causes a C02 saving. 
         [0014]    According to one exemplary embodiment of the invention, the internal combustion engine is dragged by the electric motor such that the exhaust gases of the internal combustion engine have a higher temperature than during operation of the internal combustion engine without the electric motor at the same revolution rate. The exhaust gas temperature is thereby increased because a greater proportion of the energy of combustion of the internal combustion engine is released as thermal energy. 
         [0015]    According to another exemplary embodiment of the invention the method also comprises the following step: selecting injection parameters and/or ignition parameters of the internal combustion engine such that independent operation of the internal combustion engine is no longer possible. Injection and ignition parameters can be e.g. the injection quantity, injection duration, injection interval, composition of the injected fuel mixture, and the ignition time. A higher exothermic rise in the exhaust gas is guaranteed by selecting said parameters regardless of how the engine is running. 
         [0016]    For example the ignition parameters and the injection parameters can be selected independently of the torque generation of the internal combustion engine such that the highest possible temperature of the exhaust gases is guaranteed. 
         [0017]    According to another exemplary embodiment of the invention, the specifiable revolution rate as well as the injection parameters and/or ignition parameters can be selected or adjusted such that the temperature of the exhaust gases is increased at the cost of the torque generating proportion of the combustion of the internal combustion engine in comparison with the operation of the internal combustion engine without an electric motor. 
         [0018]    According to another exemplary embodiment of the invention, the method also comprises the step of determining a current temperature in the exhaust gas aftertreatment system. The current temperature can e.g. be determined at a component of the exhaust gas aftertreatment system, such as e.g. at a catalyzer, or at a lambda probe before the exhaust gas aftertreatment system. The current temperature can be determined directly with the aid of sensors or even indirectly, for example by using the cooling water temperature in the area of the exhaust gas aftertreatment system. The current temperature can for example be measured continuously or at regular intervals. The current temperature measurement values can be forwarded to a control device for evaluation. 
         [0019]    According to another exemplary embodiment of the invention, the method also comprises the following steps: comparing the current temperature with a specifiable target temperature value; ending the dragging process of the internal combustion engine by the electric motor once the current temperature corresponds to or exceeds the specifiable target temperature value. 
         [0020]    The target temperature value can e.g. correspond to an optimal working temperature of the exhaust gas aftertreatment system or of components of the exhaust gas aftertreatment system. It can be adjusted and stored e.g. in a control device, for example of a hybrid vehicle. For example, the specifiable target temperature value can lie in the region of 250° C. The control device can carry out a comparison between the current measured temperature value and the specified target temperature value and can end the dragging process accordingly once the target temperature value is reached. After that a change to “normal mode” can take place. The “normal mode” can be operation of a vehicle only by means of an internal combustion engine or only by means of an electric motor. The “normal mode” or a hybrid mode can also be by means of a combination of electric motor and internal combustion engine. 
         [0021]    According to another exemplary embodiment of the invention, the method also comprises the following step: ending the dragging process of the internal combustion engine by the electric motor once a specifiable time interval since the detection of a need to heat the exhaust gas aftertreatment system has been exceeded. 
         [0022]    The dragging process can also be terminated independently of a measurement value of the current temperature at the exhaust gas aftertreatment system. If e.g. the optimal working temperature of the exhaust gas aftertreatment system has not yet been reached after a predetermined time period, then the process is terminated and changed to “normal mode”. The specifiable time interval can e.g. be 2 to 5 minutes since a cold start of the internal combustion engine. 
         [0023]    According to a second aspect of the invention, a control device is described that is implemented to carry out the method described above. For this purpose the control device can be connected by lines to an internal combustion engine, an electric motor and sensors, such as for example temperature sensors. The control device is implemented here to receive signals, such as e.g. measurement values of the current temperature, and to control and regulate the operation of the internal combustion engine and of the electric motor. For this purpose, the control device can, for example, specify the specifiable revolution rate of the internal combustion engine and adjust the injection and ignition parameters. 
         [0024]    According to a third aspect of the invention, a computer program element is described that is designed to implement the method described above if it is executed on a processor, for example on a control device. 
         [0025]    According to a fifth aspect of the invention a computer-readable medium is described, wherein the program element described above is stored on the medium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Other features and advantages of the invention are apparent to the person skilled in the art from the following description of exemplary embodiments, which however are not to be construed as limiting the invention, with reference to the accompanying figures. 
           [0027]      FIG. 1  shows a schematic diagram of the method according to an exemplary embodiment of the invention 
           [0028]      FIG. 2  shows schematically a hybrid vehicle system with a control unit, which is suitable to implement a method according to an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    All figures are only schematic representations of devices according to the invention and their components or of process steps. In particular, distances and dimensional relationships are not reproduced to scale in the figures. In the figures corresponding elements are provided with the same reference numbers. 
         [0030]    In  FIG. 1  a diagram of the method according to an exemplary embodiment of the invention is illustrated schematically. In step S 1  an internal combustion engine  3  is started. In step S 3  the need to heat the exhaust gas aftertreatment system is detected. A possible cause of the need for heating can for example be a cold start of the internal combustion engine  3 . For detection of the need to heat the exhaust gas aftertreatment system  15 , the current temperature of the exhaust gas aftertreatment system  15  can be measured and compared with a target temperature value, similarly to as in step S 9   a . Alternatively, a cold start can be detected directly on the internal combustion engine. If the system determines that the exhaust gas aftertreatment system  15  must be heated, then in step S 5  the electric motor  5  is controlled such that it drags or drives the internal combustion engine  3 . Here the electric motor  5  is regulated such that it operates the internal combustion engine  3  with a predefined torque. 
         [0031]    In step S 7  the injection and ignition parameters of the internal combustion engine  3  are also selected or adjusted such that the exhaust gas aftertreatment system  15  and in particular the catalyzer  17  disposed therein are optimally heated. The injection and ignition parameters are selected such that the internal combustion engine  3  can no longer operate independently. The displacement of the injection and ignition parameters, regardless of how the engine  3  is running, causes an increased rise of the exhaust gas temperature. The increased temperature causes the catalyzer  17  and the lambda probe  19  before the exhaust gas aftertreatment system  15  to reach the optimal working temperature faster. Thus with the aid of an electric motor  5  the so-called light-off time is reduced and the exhaust gas emissions are reduced. 
         [0032]    In step S 9  different process parameters can be interrogated. Steps S 9   a  to S 9   c  can be carried out in parallel with each other or alternatively to each other. In step S 9   a  the current temperature of the exhaust gas aftertreatment system  15  and especially of the catalyzer  17  are determined and compared with a target temperature value. If the current temperature value is below the target temperature value, then as indicated by the arrow the process can be continued, i.e. steps S 5  and S 7  are repeated. For this purpose, e.g. the electric motor  5  and the injection and ignition parameters of the internal combustion engine  3  can be readjusted with the aid of a control device  1 . If the current temperature value of the exhaust gas aftertreatment system  15  corresponds to the specified target temperature value or if it is higher than the target temperature value, then in step S 11  the dragging process by the electric motor  5  is terminated and a “normal” driving mode is initiated in the hybrid vehicle. A normal driving mode here can be e.g. operation with the internal combustion engine. An adequate proportion of the energy of combustion of the internal combustion engine  3  can thereby be provided for the torque generation, so that independent operation of the internal combustion engine  3  is possible. Alternatively, in “normal mode” the vehicle is driven only by the electric motor  5  or by a combination of the electric motor and the internal combustion engine. 
         [0033]    Additionally or alternatively to step S 9   a,  in step S 9   b  it is determined how much time has elapsed since the determination of the need to heat the exhaust gas aftertreatment system  15 , i.e. for example since a cold start. The determined time value is compared with a specifiable time interval. If the determined time value is less than the specified time interval, then steps S 5  and S 7  are repeated. If the determined time value is equal to or greater than the specified time interval, then the dragging process is terminated and the normal driving mode is initiated. 
         [0034]    Another additional or alternative step S 9   c  can be provided. In step S 9   c  a check is carried out as to whether the battery of the electric motor  5  still has sufficient energy to be able to continue the process. In the event that there is sufficient energy the process is continued and steps  55  and S 7  are repeated. If sufficient energy is no longer available, then a change is made to the normal driving mode using the internal combustion engine  3 . 
         [0035]    The described method can be combined with other heating measures, such as for example catalyzer heating measures. For example, in addition optimization of the working temperature can take place by configuring the position and the distribution of the individual injection quantities for the exhaust gas temperature. Said additional method for adjusting the optimal temperature of the exhaust gas aftertreatment system is referred to as HSP (Homogenous Split). 
         [0036]    In  FIG. 2  a hybrid vehicle system with a control unit  1  is illustrated schematically, which is suitable for carrying out the method described above. The hybrid vehicle system comprises, besides the control device  1 , an internal combustion engine  3  and an electric motor  5 . The internal combustion engine  3  and the electric motor  5  can be connected to each other by means of a clutch  11 . An exhaust gas aftertreatment system  15  is connected to the internal combustion engine  3 . The exhaust gas aftertreatment system  15  comprises a catalyzer  17 . A lambda probe  19  is also provided before the exhaust gas aftertreatment system. The hybrid vehicle system also comprises a converter  9 , an automatic gearbox  7  and an axle with vehicle wheels  13 . The control device  1  can be connected to all the mentioned components of the hybrid vehicle system and can control or regulate them. In particular, the control device  1  can determine the current temperature value of the exhaust gas aftertreatment system  15  or of the lambda probe  19 . The control device  1  can also regulate the injection and ignition parameters of the internal combustion engine  3  and can adjust or regulate the revolution rates of the internal combustion engine  3  and of the electric motor  5 . 
         [0037]    The control device  1  is designed to control the electric motor  5  such that it drags the internal combustion engine  3  following a cold start and thereby maintains it at a specifiable revolution rate. In this way the hot exhaust gases of the internal combustion engine  3  rapidly bring the exhaust gas aftertreatment system  15  to an optimal working temperature as required. This enables the C02 emissions to be reduced. 
         [0038]    In conclusion it is noted that expressions such as “having” or similar should not exclude the ability to provide other elements or steps. Furthermore, it should be noted that “one” does not exclude any number. Moreover, connections with the various embodiments of described features can be combined as desired.