Method for detecting the icing of a particulate filter, in particular a gasoline particulate filter

Abstract

Method for detecting the icing of a particulate filter (8), in particular a gasoline particulate filter (8), wherein a temperature of the exhaust gas flow (2) flowing through the particulate filter is determined, wherein icing of the particulate filter (8) is detected on the basis of the determined temperature of the exhaust gas flow (2), characterized in that the temperature of the exhaust gas flow (2) upstream of the particulate filter (8) and the temperature of the exhaust gas flow (2) downstream of the particulate filter (8) are determined, wherein a heat input into the particulate filter (8) and the amount of water contained in the particulate filter (8) are determined on the basis of the determined temperature difference, wherein the existing aggregate states of the water in the particulate filter (8) are calculated by balancing the amount of heat.

Description

[0001] The invention relates to a method for detecting the icing of a gasoline particulate filter with the features of the preamble of patent claim 1.

[0002] When fuels are burned, process water is produced that collects in the components of the exhaust system if insufficient heat is available to remove this water. If the ambient temperature drops, this water can freeze, and the ice that now forms in the exhaust system can lead to high exhaust backpressure. If the combustion engine can no longer perform the necessary expulsion work against the exhaust backpressure, the engine will die. The gasoline particulate filter has several substrate channels that are alternately closed. Since the gas must diffuse through the wall, icing of the substrate channels leads to a disproportionately high increase in flow resistance and, as a result, to high backpressure.

[0003] An exhaust heat recovery control device is known from DE 10 2015 201 495 A1. This device comprises a heat recovery setting unit for setting the amount of exhaust heat recovered by the exhaust heat recovery control device and a control unit for controlling the heat recovery setting unit. This is intended to prevent or suppress freezing in an exhaust pipe. For this purpose, a vehicle's driving history is evaluated, and freezing in the exhaust pipe is predicted. If, for example, it is determined based on the driving history that freezing is inevitable, freezing in the exhaust can be counteracted in advance by controlling the heat recovery setting unit to reduce or limit the amount of recovered exhaust heat. If, on the other hand, it is determined based on the driving history that freezing is not likely to occur, more exhaust heat can be recovered.The control unit is connected to a water temperature sensor and an outside air temperature sensor. The control unit controls the heat recovery adjustment unit based on the detection results of the water temperature sensor and the outside air temperature sensor. It compares whether the previous driving time, as the driving history, is less than or equal to a predefined reference time. If the previous driving time is less than or equal to the predefined reference time, there is a correspondingly high probability that the inside of the exhaust pipe will freeze.

[0004] JP 2006-283 579 A also discloses the control of a heat recovery unit depending on the ambient temperature. The thermal energy is recovered from the exhaust gas stream using a heat exchanger. The ambient temperature and the exhaust gas temperature are measured. If the ambient temperature falls below zero degrees, freezing of the process water in the exhaust system is predicted. Furthermore, the cooling water temperature is measured and taken into account.

[0005] JP 2008-190 341 A describes a method designed to prevent icing. There is no detection of whether the particulate filter is icy.

[0006] DE 10 2014 209 960 A1 discloses performing a heat balance using two temperature sensors. This determines whether liquid water accumulates in an SCR catalyst after a cold start. The SCR catalyst can be applied as a coating to a particulate filter. There is no detection of whether the particulate filter is frozen.

[0007] DE 10 2006 028 701 A1 discloses a particulate filter diagnosis system that includes a pressure difference sensor. It checks whether the pressure difference sensor is icing up. There is no detection of whether the particulate filter is icing up.

[0008] From the generic JP 2013-160 208 A, methods are known for determining whether frozen water or water in liquid form is present within a particulate filter. The differential pressure upstream and downstream of the particulate filters is measured. A temperature sensor measures the exhaust gas temperature of the particulate filter. Based on these two measured values, it is determined whether ice or water is present in the particulate filter. When the water in the particulate filter freezes, the differential pressure increases, which detects icing.

[0009] The invention is based on the object of improving the process.

[0010] The problem underlying the invention is now solved by a method having the features of patent claim 1.

[0011] In a preferred embodiment, the temperature of the exhaust gas flow upstream of the particulate filter is measured using a first temperature sensor, and the temperature of the exhaust gas flow downstream of the particulate filter is measured using a second temperature sensor. Based on the measured temperature difference, the heat input into the particulate filter and the heat input into the water in the particulate filter are determined, with the existing aggregate states of the water in the particulate filter being calculated.

[0012] Alternatively, the temperature of the exhaust gas flow upstream of the particulate filter and / or the temperature downstream of the particulate filter can be determined by a model. In particular, it is possible to mathematically determine the temperature of the exhaust gas flow upstream of the particulate filter using a model and to measure the temperature downstream of the particulate filter using a temperature sensor. In this embodiment, only one temperature sensor is present.

[0013] Preferably, a volume flow through the particulate filter is recorded, which is also used to calculate the heat input. The larger the volume flow, the higher the energy input into the particulate filter.

[0014] The amount of water present in the particulate filter is determined, whereby the water quantity is differentiated according to its physical state. The physical parameters for the ingress and egress of water in the exhaust system are calculated. The method is based on a model approach with which the existing physical states of the water can be determined in parallel. The amount of heat is balanced, whereby the energy input into the individual physical states is calculated. By balancing the amount of heat, the water components can be assigned to the physical states and converted into one another. In particular, this method is continued continuously and thus also takes into account longer cooling phases during which changes in physical state can occur. Preferably, the vehicle's downtime is determined and taken into account when determining the physical states.

[0015] In particular, the ambient temperature is determined, whereby, for example, after a longer period of inactivity of the vehicle at an ambient temperature above zero, it can be assumed that no ice is present in the particulate filter.

[0016] Using defined parameters, appropriate information entries can be generated for a workshop to better localize potential customer complaints. A thermodynamic assessment of the aggregate states is performed in the model, which enables the development of an empirical parameterization while simultaneously increasing accuracy. The method enables the precise determination of the point in time at which the water in the exhaust system has at least completely liquefied. This is achieved by differentiating the previously calculated amount of water in the particulate filter into its possible aggregate states using thermodynamic calculation principles. These principles relate to the thermodynamic energy conversion processes and are described as thermodynamic states.

[0017] The energy required for a corresponding temperature change until a change in state of matter occurs can be calculated as the product of the specific heat capacity c of ice or water, depending on the prevailing state of matter, the stored water mass m in the particulate filter, and the required temperature change dT: Q (i) = c*m*dT. The index i indicates the calculation step.

[0018] The energy requirement for a change of state can be expressed as the product of the enthalpy of fusion q(s) or enthalpy of vaporization q(v) and the water mass m in the particle filter: Q (i+1) = q (s, v)*m.

[0019] The total energy required for the change of state is Q GES =Q(i)+Q(i+1).

[0020] Furthermore, the energy required to heat the particulate filter itself is calculated and added to the energy required for the change in state. These calculations are performed in parallel for all state changes from solid to liquid or from liquid to gas. In the event of icing of the particulate filter, the calculation of the required energy is used and set as a threshold. Once this threshold is reached, it can be assumed that there is no ice or liquid water in the particulate filter, and the discharge can continue to be calculated normally.

[0021] Targeted treatment of the current water condition in the particulate filter can be carried out. The measures implemented can be specifically selected so that, for example, they only detect the discharge of ice and liquid water and do not generally last longer than necessary.

[0022] There are now numerous possibilities for advantageously designing and developing the method according to the invention. For this purpose, reference is first made to the claims subordinate to claim 1. A preferred embodiment of the invention will be explained in more detail below with reference to the drawing and the accompanying description. The drawing shows: Fig. 1 shows a highly schematic internal combustion engine with an exhaust system, Fig. 2 shows a diagram showing the amount of water in solid and liquid form in the gasoline particulate filter of the exhaust system over time.

[0023] Fig. 1 shows an internal combustion engine 1 having an exhaust system 2. The exhaust system has a first lambda probe 4 downstream of the cylinders 3, a catalytic converter 5, in particular a three-way catalytic converter 5, further downstream a second lambda probe 6, and further downstream a first temperature sensor 7, further downstream a gasoline particulate filter 8, and downstream of the gasoline particulate filter 8 a second temperature sensor 9.

[0024] The first temperature sensor 7 is arranged upstream of the gasoline particulate filter 8, and the second temperature sensor 9 is arranged downstream of the gasoline particulate filter 8. By measuring the temperature of the exhaust gas stream 2 upstream of the gasoline particulate filter 8 and downstream of the gasoline particulate filter 8, it is possible to determine how much thermal energy has been extracted from the exhaust gas by the gasoline particulate filter and the water contained therein. Using the present method, the amount of water present in the gasoline particulate filter 8 can be determined and differentiated according to its aggregate state. This determination is performed continuously.

[0025] When the car is started for the first time after production or when a new gasoline particulate filter has been installed, there is initially no water present in the gasoline particulate filter. From then on, the physical boundary conditions for water ingress and egress are calculated based on the values from the two temperature sensors 7 and 9.

[0026] The method determines the states of aggregation of the water present in the gasoline particulate filter 9. By balancing the heat quantity, the water components can be assigned and converted into one another. When the vehicle is parked, a parking time is preferably determined. This parking time is also taken into account when determining the water quantity in the gasoline particulate filter 8 and also the state of aggregation of the water in the gasoline particulate filter 8. This also takes into account longer cooling phases during which changes in state of aggregation can occur. As a further parameter for determining the states of aggregation, the ambient temperature is preferably measured using a sensor (not shown here).

[0027] For example, if the ambient temperature is below 0 degrees and a longer shutdown time has been detected, it can be assumed that the water in the gasoline particulate filter 8 is frozen.

[0028] In Fig. 2, the amount of water in the solid state, i.e. ice, and in the liquid state, is plotted in the form of curves 10 and 11. Initially, all of the water in the gasoline particulate filter 8 is frozen. As time goes on, an increasing proportion of the ice liquefies until finally all of the water is only in liquid form. Upon further heating, the liquid water evaporates and changes to the gaseous state, being carried out of the gasoline particulate filter 8 by the exhaust gas stream 2. These three phases of water, namely solid, i.e. ice, liquid and gaseous, are modeled using the energy analysis described above. This improves the detection of icing of the gasoline particulate filter 8. LIST OF REFERENCE SYMBOLS 1 internal combustion engine 2 exhaust system 3 cylinders 4 Lambda sensor 5 Catalyst 6 Lambda sensor 7 Temperature sensor 8 gasoline particulate filters 9 Temperature sensor 10 Amount of ice in the gasoline particulate filter 11 Amount of liquid water in the gasoline particulate filter

Claims

[1] Method for detecting the icing of a particle filter (8), in particular a gasoline particle filter (8), wherein a temperature of the exhaust gas flow (2) flowing through the particle filter is determined, wherein icing of the particle filter (8) is detected on the basis of the determined temperature of the exhaust gas flow (2), characterized by that the temperature of the exhaust gas flow (2) upstream of the particle filter (8) and the temperature of the exhaust gas flow (2) downstream of the particle filter (8) are determined, wherein on the basis of the determined temperature difference a heat input into the particle filter (8) and the quantity of water contained in the particle filter (8) are determined, wherein the existing aggregate states of the water in the particle filter (8) are calculated by balancing the quantity of heat. [2] Method according to claim 1, characterized bythat the energy requirement for the temperature change up to a change in state of aggregation is determined, whereby the product of the specific heat capacity c of ice or water, depending on which state of aggregation prevails, the stored water mass m in the particle filter and the necessary temperature change dT is calculated. [3] Method according to claim 1, characterized by that the energy requirement for the change of state is determined, whereby the energy requirement for a change of state is calculated as the product of the enthalpy of fusion q(s) or the enthalpy of vaporization q(v) and the water mass m in the particle filter. [4] Method according to one of the preceding claims, characterized by that in the event of the particulate filter becoming icy, the energy required to melt the ice is calculated. [5] Method according to one of the preceding claims, characterized bythat the energy required to heat the particulate filter (8) itself is calculated. [6] Method according to one of the preceding claims, characterized by that a volume flow through the particle filter (8) is recorded, which is also used to calculate the heat input. [7] Method according to one of the preceding claims, characterized by that the ambient temperature is determined and taken into account when calculating the states of matter. [8] Method according to one of the preceding claims, characterized by that the downtime of the motor vehicle is determined and taken into account when calculating the aggregate states. [9] Method according to one of the preceding claims, characterized by that the temperature of the exhaust gas flow (2) upstream of the particle filter (8) is measured by means of a temperature sensor (7). [10] Method according to one of the preceding claims, characterized bythat the temperature of the exhaust gas flow (2) downstream of the particle filter (8) is measured by means of a temperature sensor (9). [11] Method according to one of the preceding claims, characterized by that the temperature of the exhaust gas flow (2) before the particle filter (8) and / or the temperature after the particle filter (8) is / are determined by a model.

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