Method for heating an exhaust system

Abstract

A method for heating an exhaust system downstream from an internal combustion engine using an electrical heating device. The method includes an ascertainment of a current temperature in the exhaust system, an ascertainment of a current temperature of the electrical heating device and a fluid mass flow flowing through the electrical heating device, an ascertainment of a heating requirement based on the ascertained current temperature and a target temperature, a calculation of a required amount of heat depending on the heating requirement and an amount of energy required to heat up the electrical heating device, taking into account a heat input into the fluid mass flow to be expected at the ascertained current temperature of the electrical heating device, and a control of the electrical heating device to generate the calculated amount of heat. A computing unit and a computer program are also described.

Claims

1. A method for heating an exhaust system downstream of an internal combustion engine using an electric heating device, comprising the following steps: ascertaining a current temperature in the exhaust system; ascertaining a current temperature of the electrical heating device and a fluid mass flow flowing through the electrical heating device; ascertaining a heating requirement based on the ascertained current temperature in the exhaust system and a target temperature, calculating a required amount of heat depending on the heating requirement and an amount of energy required for heating the electrical heating device, taking into account a heat input into the fluid mass flow to be expected at the ascertained current temperature of the electrical heating device; and controlling the electric heating device to generate the calculated amount of heat.

2. The method according to claim 1, wherein: (i) the ascertainment of the current temperature in the exhaust system and/or the heating device, and/or (ii) the calculation of the required amount of heat is carried out based on a temperature model of the exhaust system.

3. The method according to claim 1, further comprising: controlling a fluid flow for transporting heat from the heating device to a component of the exhaust system to be heated.

4. The method according to claim 3, wherein the component to be heated includes a catalyst and/or a particulate filter.

5. The method according to claim 3, wherein the fluid flow for transporting the heat from the heating device is controlled when the heating device reaches a predeterminable minimum temperature.

6. The method according to claim 1, wherein the target temperature is ascertained depending on one or more operating parameters of the exhaust system.

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

8. A computing unit configured to heat an exhaust system downstream of an internal combustion engine using an electric heating device, the computing unit configured to: ascertain a current temperature in the exhaust system; ascertain a current temperature of the electrical heating device and a fluid mass flow flowing through the electrical heating device; ascertain a heating requirement based on the ascertained current temperature in the exhaust system and a target temperature, calculate a required amount of heat depending on the heating requirement and an amount of energy required for heating the electrical heating device, taking into account a heat input into the fluid mass flow to be expected at the ascertained current temperature of the electrical heating device; and control the electric heating device to generate the calculated amount of heat.

9. A non-transitory machine-readable storage medium on which is stored a computer program for heating an exhaust system downstream of an internal combustion engine using an electric heating device, the computer program, when executed by a computer, causing the computer to perform the following steps: ascertaining a current temperature in the exhaust system; ascertaining a current temperature of the electrical heating device and a fluid mass flow flowing through the electrical heating device; ascertaining a heating requirement based on the ascertained current temperature in the exhaust system and a target temperature, calculating a required amount of heat depending on the heating requirement and an amount of energy required for heating the electrical heating device, taking into account a heat input into the fluid mass flow to be expected at the ascertained current temperature of the electrical heating device; and controlling the electric heating device to generate the calculated amount of heat.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an arrangement with an internal combustion engine and an exhaust system, as may be the basis of the present invention.

(2) FIG. 2 shows an example embodiment of a method according to the present invention schematically in the form of a simplified flow chart.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(3) By way of example, the following description describes an embodiment of the present invention based on an exhaust system of a gasoline engine with 3-way catalysts (TWCs) used therein.

(4) However, it should be noted that the proposed method according to the present invention 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.

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

(6) 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.

(7) 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.

(8) 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.

(9) 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 present invention will be described here using an example with a temperature-based control system.

(10) In FIG. 2, an advantageous embodiment of a method according to the present invention is shown schematically in the form of a simplified flow chart and designated 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.

(11) 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 ascertained based on sensors and/or models.

(12) 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.

(13) 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 ascertained in a step Pwr{circumflex over ()}Max.

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

(15) The desired heating power is compared with the maximum permissible heating power in a step Min. The smaller of the two ascertained 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.

(16) Before the comparative or minimum step Min is carried out, the desired heating power Pwr{circumflex over ()}Des is reduced by the amount which results from the heat transfer from the heating disk to the exhaust gas mass flow flowing toward it under the current operating parameters. For this purpose, a temperature difference between the exhaust gas upstream from the heating disk (t_EHC{circumflex over ()}Us) and the heating disk itself (t_EHC) is ascertained (link in FIG. 2) and multiplied by the heat transfer surface of the heating disk A and the heat transfer coefficient , which depends on the heating disk temperature t_EHC and the exhaust gas mass flow dm_Exh (links x in FIG. 2). The correction value obtained in this manner is subtracted from the value of the desired heating power ascertained as explained above (link in FIG. 2) to obtain a corrected desired heating power.

(17) Optionally, the corrected desired heating power as ascertained in the step Pwr{circumflex over ()}Des can be further corrected (link + in FIG. 2) before carrying out the comparison step Min by means of a controller value, which is ascertained 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.

(18) 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, . . . ).

(19) The method 200 has been described here with a focus on the heating of the catalysts in a cold start and keeping the catalysts warm during further operation. However, the method 200 can also be transferred to further areas, such as supporting particulate filter regeneration or NOx catalyst regeneration. Furthermore, to increase the emission robustness, the method 200 can advantageously also be used outside of catalyst heating or regeneration requirements in so-called normal operation to keep the downstream catalyst at a lower base temperature if applicable. If necessary, separate heating pane setpoints (target temperatures) can be defined for fine optimization in a such normal or regeneration mode.