METHOD FOR HEATING AN EXHAUST SYSTEM

Abstract

A method (200) for heating an exhaust system (120) downstream of an internal combustion engine (1) by means of an electric heating device (14, 15). In one example, the method includes determining a current temperature (t_EHC, t_EHC{circumflex over ( )}Us, t_Cat) in the exhaust system (120), determining a heating demand (t_EHC{circumflex over ( )}Des) based on the determined current temperature (t_Cat) and a target temperature, calculating a required amount of heat (Pwr{circumflex over ( )}Des) on the basis of the heating demand and an amount of energy required to heat the electric heating device (14, 15), and controlling (Pwr{circumflex over ( )}Req) the electric heating device (14, 15) to generate the calculated amount of heat.

Claims

1. A method (200) for heating an exhaust system (120) downstream of an internal combustion engine (1) by means of an electric heating device (14, 15), the method comprising: determining a current temperature (t_EHC, t_EHC{circumflex over ( )}Us, t_Cat) in the exhaust system (120), determining a heating demand (t_EHC{circumflex over ( )}Des) on the basis of the determined current temperature (t_Cat) and a target temperature, calculating a required amount of heat (Pwr{circumflex over ( )}Des) on the basis of the heating demand and an amount of energy required to heat the electric heating device (14, 15), and controlling (Pwr{circumflex over ( )}Req) the electric heating device (14, 15) to generate the calculated amount of heat.

2. The method (200) according to claim 1, wherein determining the current temperature (t_EHC, t_EHC{circumflex over ( )}Us, t_Cat) and/or calculating the required amount of heat (Pwr{circumflex over ( )}Des) is carried out on the basis of a temperature model of the exhaust system (120).

3. The method (200) according to claim 1, further comprising controlling a fluid flow (10) for transporting heat from the heating device (14, 15) to a component (11, 12, 13) of the exhaust system (120) to be heated.

4. The method (200) according to claim 3, wherein the component (11, 12, 13) to be heated comprises a catalyst and/or a particulate filter.

5. The method (200) according to claim 3, wherein the fluid flow (10) for extracting heat from the heating device (14, 15) is controlled if the heating device (14, 15) reaches a predeterminable minimum temperature.

6. The method (200) according to claim 1, wherein the target temperature is determined on the basis of one or more operating parameters of the exhaust system (120).

7. The method (200) according to claim 6, wherein the one or more operating parameters of the exhaust system (120) comprise a pollutant concentration in the exhaust system and/or a pressure drop within the exhaust system and/or an exhaust mass flow (dm_Exh) in the exhaust system and/or an ambient temperature.

8. A system for controlling an exhaust system (120) located downstream of an internal combustion engine (1), the system comprising: an electric heating device (14, 15); and a computer configured to: determine a current temperature (t_EHC, t_EHC{circumflex over ( )}Us, t_Cat) in the exhaust system (120), determine a heating demand (t_EHC{circumflex over ( )}Des) on the basis of the determined current temperature (t_Cat) and a target temperature, calculate a required amount of heat (Pwr{circumflex over ( )}Des) on the basis of the heating demand and an amount of energy required to heat the electric heating device (14, 15), and control (Pwr{circumflex over ( )}Req) the electric heating device (14, 15) to generate the calculated amount of heat.

9. A non-transitory, computer-readable storage medium containing instructions that when executed by aa computer cause the computer to control an exhaust system (120) located downstream of an internal combustion engine (1) and having an electric heating device (14, 15), by: determining a current temperature (t_EHC, t_EHC{circumflex over ( )}Us, t_Cat) in the exhaust system (120), determining a heating demand (t_EHC{circumflex over ( )}Des) on the basis of the determined current temperature (t_Cat) and a target temperature, calculating a required amount of heat (Pwr{circumflex over ( )}Des) on the basis of the heating demand and an amount of energy required to heat the electric heating device (14, 15), and controlling (Pwr{circumflex over ( )}Req) the electric heating device (14, 15) to generate the calculated amount of heat.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further advantages and embodiments of the invention can be found in the description and the accompanying drawing.

[0024] The invention is illustrated schematically in the drawing on the basis of an embodiment and is described below with reference to the drawing.

[0025] FIG. 1 shows an arrangement with an internal combustion engine and an exhaust system, as may be the basis of the invention.

[0026] FIG. 2 shows an embodiment of a method according to the invention schematically in the form of a simplified flow chart.

DETAILED DESCRIPTION

[0027] By way of example, the following description describes an embodiment of the invention based on an exhaust system of a gasoline engine with 3-way catalysts (TWCs) used therein. However, it should be noted that the proposed method is equally suitable for diesel or other internal combustion engines, e.g., gas or H2 burners. Here, the respective burner-specific catalysts are then used instead of a TWC, e.g., oxidation catalyst, SCR, particulate filter, NSC, etc.

[0028] In FIG. 1, an arrangement with an exhaust system as can be used within the framework of the invention, for example a vehicle, is shown schematically and designated overall with the number 100.

[0029] The vehicle 100 comprises an internal combustion engine 1 used to drive wheels 140 of the vehicle 100, as well as an exhaust system 120 with a plurality of catalysts 11, 12, 13 arranged downstream of the internal combustion engine 1. In the example shown, sensors 17, 18 are arranged downstream of each of the catalysts 11, 12 and are each connected in a data-conducting manner to a computing unit 20, for example a control unit of the vehicle 100. The sensors can detect operating parameters of the exhaust system 120, such as temperatures, exhaust gas compositions, exhaust gas mass flows or the like. Of course, the positions of the sensors 17, 18 shown should only be understood as examples. Furthermore, the number of sensors is also not limited to the two shown. Rather, more or fewer sensors may also be provided.

[0030] In the example shown, the computing unit 20 is further connected in a data-conducting manner to the internal combustion engine 1 and to external electric heating devices 14, 15, each of which is associated with one of the catalysts 11, 12, 13. In particular, the electric heating devices 14, 15 may also be arranged directly in the catalyst or within a housing of the catalyst. It should be noted here that at least one electric heating device is required within the framework of the present invention, but a plurality of electric heating devices, as shown in FIG. 1, can of course be used side-by-side and controlled, for example, in each case analogously to one another. In particular, when a plurality of heating devices is used, each can be operated to account only for the heating requirements of components located directly downstream of it and upstream of the next heating device.

[0031] Exhaust gas 10 generated by the internal combustion engine 1 is successively fed to the catalysts 11, 12, 13 in order to be purified or decontaminated in them. Each of the catalysts 11, 12, 13 can be provided for a particular decontamination or for a plurality of simultaneous decontaminations. For example, a first catalyst 11, which can be located close to the internal combustion engine 1, may be a three way catalyst (TWC), while a second catalyst 12 and third catalyst 13 may comprise other catalysts and/or purification components such as NOx storage catalysts, SCR catalysts, particulate filters, or the like. However, the second and third catalysts 12, 13 may also comprise one or more additional TWCs. Furthermore, the first catalyst 11 can also comprise one or more other purification components and does not necessarily have to be in the form of a TWC.

[0032] Depending on the type of catalyst, each of the catalysts 11, 12, 13 has a specific thermal working range, also referred to as a conversion window. For effective conversion, a predeterminable minimum temperature, also known as the light-off temperature, must be reached. Above the light-off temperature, a conversion of the various pollutants into less harmful substances takes place. However, if necessary, an increase in effectiveness can still be achieved if the relevant catalyst is operated at a temperature that is higher than the light-off temperature. In such a case, a set temperature is advantageously specified for the relevant catalyst 11, 12, 13. As described at the beginning, a control system can generally also be based on thermally active volume fractions of the cleaning components. However, the invention will be described here using an example with a temperature-based control system.

[0033] In FIG. 2, an advantageous embodiment of a method according to the invention is shown schematically in the form of a simplified flow chart and denoted by the number 200. For the sake of simplicity, only the control system of a single electric heating device 14 is described here; if there is a plurality of heating devices, each can be operated similarly to the method described here.

[0034] The method 200 uses as input variables temperatures of catalyst(s), t_Cat, exhaust gas upstream of the electric heating device, t_EHC{circumflex over ( )}Us, and the heating device, t_EHC, along with an exhaust gas mass flow, dm_Exh. Such input variables can be determined based on sensors and/or models.

[0035] Based on the current catalyst temperature t_Cat, a target temperature for the exhaust gas leaving the heating disk is calculated in a step t_EHC{circumflex over ( )}Des. The minimum operating temperature (“light-off temperature”) required in the relevant catalyst is taken into account here.

[0036] Based on the exhaust gas mass flow dm_Exh, the exhaust gas temperature upstream of the heating disk t_EHC{circumflex over ( )}Us and the current temperature of the heating disk t_EHC, a maximum permissible heating power for the heating device 14 is determined in a step Pwr{circumflex over ( )}Max.

[0037] Furthermore, based on the input variables used in the step Pwr{circumflex over ( )}Max and the target temperature determined in the step t_EHC{circumflex over ( )}Des, a heating power desired to achieve the target temperature as efficiently as possible is determined in a step Pwr{circumflex over ( )}Des.

[0038] The desired heating power is compared with the maximum permissible heating power in a step Min. The smaller of the two determined heating powers is then output as the heating power requirement and the heating disk is controlled according to the heating power requirement. For this purpose, a corresponding electrical power is supplied to the heating disk from a vehicle electric system of the vehicle 100.

[0039] Optionally, the desired heating power as determined in the step Pwr{circumflex over ( )}Des can be corrected (link “+” in FIG. 2) before carrying out the comparison step Min by means of a controller value, which is determined in a step PI/PID based on a difference (link “-” in FIG. 2) between the target temperature and the current temperature of the heating disk t_EHC. However, this is not absolutely necessary due to the already very precise and robust temperature control, since, in the step PI/PID, only disturbance variables with a relatively small influence on the final exhaust gas temperature downstream of the heating disk 14 are compensated for.

[0040] It should be emphasized that the method 200 cannot be carried out exclusively with exhaust gas as the heat transfer fluid; rather, externally conveyed fluids, in particular air, can also be used. This is particularly advantageous in situations in which no exhaust gas mass flow is (yet) available, for example in situations in which the vehicle 100 is stationary and/or the internal combustion engine 1 is not being operated (e.g., prior to a departure, during electrically driven travel in hybrid vehicles, . . . ).