DE102018220403A1 - Tank ventilation system and method for determining a hydrocarbon load and / or a hydrocarbon flow in the tank ventilation system - Google Patents

Abstract

The invention relates to a tank ventilation system (20) which has an activated carbon filter (22), a tank ventilation line (23) and a tank ventilation valve (24) which is arranged in the tank ventilation line (23). A temperature sensor (41) is arranged in the tank ventilation line (23) between the activated carbon filter (22) and the tank ventilation valve (24). The invention further relates to a method for determining a hydrocarbon load on the activated carbon filter (22) and / or a hydrocarbon flow through the tank ventilation line (23) of the tank ventilation system (20). The hydrocarbon loading and / or the hydrocarbon flow are determined by an observer who uses a temperature measured by means of the temperature sensor (41) as an output variable.

Description

The present invention relates to a tank ventilation system. It also relates to a method for determining a hydrocarbon load on an activated carbon filter and / or a hydrocarbon stream through a tank ventilation line of the tank ventilation system. Furthermore, the present invention relates to a computer program that executes every step of the method and a machine-readable storage medium that stores the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method.

State of the art

Depending on the pressure and temperature conditions prevailing in the fuel tank and the composition of the fuel, hydrocarbons evaporate in a fuel tank of a motor vehicle. For reasons of environmental protection and safety, these must be fed to the internal combustion engine of the motor vehicle for combustion. For this purpose, they are usually adsorbed by means of an activated carbon filter and temporarily stored. In order to regenerate the activated carbon again and again, a line leads from the activated carbon filter into the intake manifold of the internal combustion engine. When the internal combustion engine is operating, a vacuum is created in the intake manifold, which causes air from the surroundings to flow through the activated carbon into the intake manifold. This desorbs the deposited hydrocarbons so that they can be used for engine combustion. A tank vent valve is arranged between the suction pipe and the activated carbon filter and doses this air flow. This air flow can be adapted to the operating state of the internal combustion engine via the electrical pulse duty factor and the frequency of the activation of the tank ventilation valve. With the help of the lambda control of the internal combustion engine, it is possible to draw conclusions about the hydrocarbon quantity entered and the fuel / air mixture adaptation will adapt the fuel quantity injected via the fuel injectors accordingly.

Since the hydrocarbon load of the activated carbon filter is initially unknown, the tank vent valve must be used carefully, i. H. are initially controlled with a small duty cycle and can only be opened further carefully to keep the deviations from the desired target lambda low. Stricter legal requirements as well as restrictive motor boundary conditions for activated carbon filter regeneration, however, require increasing regeneration air flows in the tank ventilation system in order to keep the evaporation emissions to hydrocarbons as low as possible. In hybrid vehicles in particular, forced activation of the internal combustion engine may be necessary in order to prevent the activated carbon filter from overflowing.

Disclosure of the invention

Conventional tank ventilation systems have an activated carbon filter, a tank ventilation line and a tank ventilation valve which is arranged in the tank ventilation line. In the present tank ventilation system, a temperature sensor is additionally arranged in the tank ventilation line between the activated carbon filter and the tank ventilation valve. This structure of the tank ventilation system is based on the knowledge that the desorption of hydrocarbons from the activated carbon filter has a cooling effect on a regeneration air flow or flushing flow which flows from the environment through the activated carbon filter and the tank ventilation valve into an intake manifold of an internal combustion engine. Depending on the hydrocarbon load of the activated carbon filter, this cooling effect is different.

If it is possible to measure the temperature of the tank ventilation line, this allows determination of a hydrocarbon load on the activated carbon filter and / or a hydrocarbon flow through the tank ventilation line of the tank ventilation system. For this purpose, a method is proposed in which the hydrocarbon loading and / or the hydrocarbon flow is determined by an observer who uses a temperature measured by means of the temperature sensor as an output variable. In control engineering, an observer is a system that reconstructs non-measurable variables from known input variables and output variables of an observed reference system. For this purpose, the observer simulates the observed reference system as a model and tracks the measurable state variables in the controller, which are therefore comparable with the reference system. In this the output variable is the temperature information. The temperature depicted by the model of the activated carbon filter is compared with the temperature measured by means of the temperature sensor and an observer error is depicted. The observer error is returned to the activated carbon filter model to compensate for the modeling inaccuracy. As a result, the state variables, which are the hydrocarbon loading of the activated carbon filter and the hydrocarbon flow through the tank ventilation line, are reconstructed.

If the hydrocarbon loading of the activated carbon filter and / or the hydrocarbon flow through the tank ventilation line is known, the tank ventilation valve can be opened quickly and, if necessary, completely, because the tank ventilation system enters the internal combustion engine Fuel quantity can be calculated precisely and quickly and can be taken into account by adjusting the fuel injector time of the internal combustion engine. Deviations in the lambda are therefore slight or are completely eliminated. Possible tank ventilation phases can be exploited well, which enables a high regeneration amount. Overflowing of the activated carbon filter under difficult boundary conditions can thus be avoided and reduced evaporative emission limit values can also be maintained.

In particular, a mass flow from the activated carbon filter, an ambient temperature and an ambient pressure are used as input variables of the observer.

The activated carbon filter can be modeled on the basis of thermodynamic relationships. The activated carbon filter is preferably modeled in the observer using a one-dimensional model. This enables the activated carbon filter in the model to be divided into several parts. Each part particularly preferably has a gas phase, an adsorbent phase and an adsorber wall phase. This makes it possible to realistically model the adsorption processes in the activated carbon filter.

It is further preferred that energy transfers and material transfers between the phases are taken into account in the model. This is important in order to realistically map the physical processes of absorption.

For the mathematical description of the activated carbon filter, it is preferred that the model takes into account a total mole balance of the gas phase, an energy balance of the gas phase, a load balance of the adsorbent phase, an energy balance of the adsorbent phase, an energy balance of the adsorber wall phase and a component mole balance for each part.

The computer program is set up to carry out every step of the method, in particular if it is executed on a computing device or an electronic control device. It enables different embodiments of the method to be implemented on an electronic control unit without having to make structural changes to it. For this purpose, it is stored on the machine-readable storage medium. By loading the computer program onto a conventional electronic control unit, the electronic control unit is obtained, which is set up to use the method to determine a hydrocarbon load on the activated carbon filter and / or a hydrocarbon flow through the tank ventilation line of the tank ventilation system.

Figure list

• 1 zeigt schematisch ein Tankentlüftungssystem gemäß einem Ausführungsbeispiel der Erfindung.
• 2 zeigt einen Beobachter, der in einem Verfahren gemäß einem Ausführungsbeispiel der Erfindung verwendet wird.
• 3 zeigt die Aufteilung eines Aktivkohlefilters in mehrere Teile in einem Modell, das in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens verwendet wird.

Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the description below.

• 1 shows schematically a tank ventilation system according to an embodiment of the invention.
• 2nd shows an observer used in a method according to an embodiment of the invention.
• 3rd shows the division of an activated carbon filter into several parts in a model that is used in an embodiment of the method according to the invention.

Embodiments of the invention

1 shows a fuel tank 10th that with a tank ventilation system 20th and an engine system 30th connected is. A connecting line 21st leads out of the fuel tank 10th into an activated carbon filter 22 so that from the fuel tank 10th escaping hydrocarbon vapors in the activated carbon filter 22 can be adsorbed. For regeneration of the activated carbon filter 22 is a tank ventilation line 23 provided in the tank vent valve 24th is arranged. An internal combustion engine 31 of the engine system 30th has an intake manifold 32 with a throttle valve 33 on. The tank ventilation line 23 ends in the intake manifold 32 between the internal combustion engine 31 and the throttle valve 33 . With the tank ventilation valve open 24th causes a vacuum in the intake manifold 32 caused by the throttle effect of the throttle valve 33 is caused that ambient air in the activated carbon filter 22 flows in, adsorbed hydrocarbons and desorbs them through the tank ventilation line 23 and the suction pipe 32 combustion in the internal combustion engine 31 feeds. This mass flow ṁ ₃₂ is also referred to as a purge flow.

Between the activated carbon filter 22 and the tank vent valve 24th is in the tank ventilation line 23 a temperature sensor 41 arranged. With this, the temperature T ₃₂ mess in the tank ventilation line 23 be measured. There is also an ambient temperature sensor 42 for measuring the ambient temperature T _U and an ambient pressure sensor 43 for measuring the ambient pressure p _U intended. All sensors 41 , 42 , 43 deliver data to an electronic control unit 50 . This also controls the tank ventilation valve 24th .

In one embodiment of the method according to the invention is in the electronic control unit 50 an observer 60 implemented, whose structure in 2nd is shown. The observer uses the Ambient temperature T _U , the ambient pressure p _U and the mass flow Ṅ ₂₃ . The latter can result from the negative pressure in the suction pressure 32 and the degree of opening of the tank ventilation valve 24th be calculated. The input variables become a reference system 61 of the activated carbon filter 22 made available, which delivers the measured temperature T ₂₃ mess as an output variable. This reference system is still in one model 62 reproduced, a modeled temperature as the output variable T ₃₂ mod in the tank ventilation line 23 delivers. By making the difference between the measured temperature T ₃₂ mess and the modeled temperature T ₂₃ mod an observer error ΔT is obtained, which is related to the model 62 is returned. This compensates for the modeling inaccuracy, so that state variables of the model 62 can be reconstructed. These state variables are the hydrocarbon loading Xj ^AS (j = hydrocarbons (HC)) of the activated carbon filter 22 and the hydrocarbon flow Ṅ _J (j = HC) through the tank ventilation line 23 . In the model 62 the activated carbon filter is modeled one-dimensionally 22 . As in 3rd is shown, the activated carbon filter 22 thereby in several parts of the same size 70 divided, numbered from 0 to N. For the parts with the numbers k-1, k and k + 1 the structure of the parts is 70 presented in detail. These each have a gas phase 71 , an adsorbent phase 72 and an adsorber wall phase 73 on. The gas phase 71 corresponds to the gas space in the activated carbon filter 22 . The adsorbent phase 72 corresponds to activated carbon. The adsorber wall phase 73 corresponds to the container wall of the activated carbon filter.

Energy transfers and material transfers between phases 71 , 72 , 73 are in 3rd shown.

The modeling is based on the thermodynamic relationships according to formulas 1 to 6. Here, formula 1 describes the total molar balance of the gas phase 71 : $$\frac{V_k^G}{R{T}_k^G}\frac{d{p}_k^G}{dt}-\frac{p_k^G{V}_k^G}{R{T}_k^G{T}_k^G}\frac{d{T}_k^G}{dt}={\dot{N}}_{k-1}-{\dot{N}}_k-{\dot{N}}_k^{ads}$$

das Gasvolumens des Teils k, $p_k^G$

beschreibt den Gasdruck im Teil k, $T_k^G$

beschreibt die Gastemperatur im Teil k, Ṅ_k-1 beschreibt den Molenstrom des Gesamtspülstroms aus dem Teil k-1, Ṅ_k beschreibt den Molenstrom des Gesamtspülstroms aus dem Teil k, R bezeichnet die universelle Gaskonstante und t bezeichnet die Zeit.Describes $V_k^G$

the gas volume of part k, $p_k^G$

describes the gas pressure in part k, $T_k^G$

describes the gas temperature in part k, Ṅ _k-1 describes the molar flow of the total purge flow from part k-1, Ṅ _k describes the molar flow of the total purge flow from part k, R denotes the universal gas constant and t denotes time.

Formula 2 gives the energy balance of the gas phase 71 again: $$-V_k^G\frac{d{p}_k^G}{dt}+\frac{p_k^G{V}_k^G}{R{T}_k^G}{\mathrm{C.}}_k^{pt}\frac{d{T}_k^G}{dt}={\dot{H}}_{k-1}-{\dot{H}}_k-{\dot{Q}}_k^{GAS}-{\dot{Q}}_k^{G\mathrm{C.}}$$

bezeichnet die Wärmekonstante der Gasphase 71 des Teils k. Weiterhin steht ${\dot{Q}}_k^{GAS}$

für die Wärmeübertragung von der Gasphase 71 in die Adsorbentphase 72 und ${\dot{Q}}_k^{GC}$

steht für die Wärmeübertragung von der Gasphase 71 in die Adsorberwandphase 73.In it Ḣ _k-1 denotes the entalpy flow from part k-1, Ḣ _k denotes the entalpies flow from part k and ${\mathrm{C.}}_k^{pt}$

denotes the heat constant of the gas phase 71 of part k. Still stands ${\dot{Q}}_k^{GAS}$

for heat transfer from the gas phase 71 into the adsorbent phase 72 and ${\dot{Q}}_k^{G\mathrm{C.}}$

stands for heat transfer from the gas phase 71 in the adsorber wall phase 73 .

Formula 3 gives the component molar balances: $$\frac{d{p}_k^G}{dt}-\frac{y{j}_k^G{p}_k^G{V}_k^G}{R{T}_k^G{T}_k^G}\frac{d{T}_k^G}{dt}+\frac{p_k^G{V}_k^G}{R{T}_k^G}\frac{dy{j}_k^G}{dt}=\dot{N}{j}_{k-1}-\dot{N}{j}_k-\dot{N}{j}_k^{ads}$$

Here yj describes the mole fraction of the respective components. j is used for component designation (e.g. HC, N ₂ , O ₂ etc.).

The energy balance of the adsorber wall results from Formula 4: $$m_k^{\mathrm{C.}}{\mathrm{C.}}_k^{\mathrm{C.}}\frac{d{T}_k^{\mathrm{C.}}}{dt}={\dot{Q}}_{k-1}^{cOnd}-{\dot{Q}}_k^{cOnd}+{\dot{Q}}_k^{AS\mathrm{C.}}+{\dot{Q}}_k^{G\mathrm{C.}}-{\dot{Q}}_k^{\mathrm{C.}\mathrm{C.}A}-{\dot{Q}}_k^{R\mathrm{C.}A}$$

die die Adsorberwandmasse des Teils k, ${\dot{Q}}_{k-1}^{cond}$

die Wärmeübertragung von der Adsorberwandphase 73 des Teils k-1 in die Adsorberwandphase 73 des Teils k, ${\dot{Q}}_k^{cond}$

bezeichnet die Wärmeübertragung von der Adsorberwandphase 73 des Teils k in die Adsorberwandphase 73 des Teils k+1, ${\dot{Q}}_k^{ASC}$

bezeichnet die Wärmeübertragung von der Adsorbentphase 72 in die Adsorberwandphase 73 im Teil k und ${\dot{Q}}_k^{CCA}$

und ${\dot{Q}}_k^{RCA}$

bezeichnet die Wärmeübertragungen (Konvektion und Wärmestrahlung) aus der Adsorberwandphase 73 in die Umgebung. $C_k^C$

bezeichnet die Wärmekonstante der Adsorberwandphase 73 im Teil k.Inscribed here $m_k^{\mathrm{C.}}$

which is the adsorber wall mass of part k, ${\dot{Q}}_{k-1}^{cOnd}$

the heat transfer from the adsorber wall phase 73 of part k-1 in the adsorber wall phase 73 of part k, ${\dot{Q}}_k^{cOnd}$

denotes the heat transfer from the adsorber wall phase 73 of part k into the adsorber wall phase 73 of part k + 1, ${\dot{Q}}_k^{AS\mathrm{C.}}$

denotes the heat transfer from the adsorbent phase 72 in the adsorber wall phase 73 in part k and ${\dot{Q}}_k^{\mathrm{C.}\mathrm{C.}A}$

and ${\dot{Q}}_k^{R\mathrm{C.}A}$

denotes the heat transfers (convection and heat radiation) from the adsorber wall phase 73 in the nearby areas. ${\mathrm{C.}}_k^{\mathrm{C.}}$

denotes the heat constant of the adsorber wall phase 73 in part k.

The loading balance of the adsorbent phase 72 results on formula 5: $$\frac{dX{j}_k^{AS}}{dt}=\frac{\dot{N}{j}_k^{ads}}{m_k^{AS}}$$

die Stoffbeladung des Aktivkohlefilters 22 im Teil k. $m_k^{AS}$

bezeichnet die Adsorbentmasse des Teils k, also die Masse an Aktivkohle.Inscribed there $X{j}_k^{AS}$

the fabric load of the activated carbon filter 22 in part k. $m_k^{AS}$

denotes the adsorbent mass of part k, i.e. the mass of activated carbon.

${\dot{H}}_k^{ads}$

bezeichnet die Adsorptionsentalpie des Teils k und $C_k^{AS}$

bezeichnet die Wärmekonstante der Adsorbentphase 72 im Teil k.The energy balance of the adsorbent phase 72 results from formula 6: $$m_k^{AS}{\mathrm{C.}}_k^{AS}\frac{d{T}_k^{AS}}{dt}={\dot{H}}_k^{ads}+{\dot{Q}}_k^{GAS}-{\dot{Q}}_k^{AS\mathrm{C.}}$$

${\dot{H}}_k^{ads}$

denotes the adsorption enthalpy of part k and ${\mathrm{C.}}_k^{AS}$

denotes the heat constant of the adsorbent phase 72 in part k.

Claims (10)

Tank ventilation system (20), comprising an activated carbon filter (22), a tank ventilation line (23) and a tank ventilation valve (24) which is arranged in the tank ventilation line (23), characterized in that in the tank ventilation line (23) between the activated carbon filter (22) and a temperature sensor (41) is arranged in the tank ventilation valve (24). Method for determining a hydrocarbon load (Xj ^AS ) of the activated carbon filter (22) and / or a hydrocarbon stream (Ṅ _J ) through the tank ventilation line (23) of the tank ventilation system (20) Claim 1 , characterized in that the hydrocarbon loading (Xj ^AS ) and / or the hydrocarbon stream (Ṅ _J ) is determined by an observer (60) who uses a temperature (T ₂₃ mess) measured by means of the temperature sensor (41) as an output variable. Procedure according to Claim 2 , characterized in that a mass flow (ṁ ₂₃ ) from the activated carbon filter (22), an ambient temperature (T _U ) and an ambient pressure (p _U ) are used as input variables of the observer (60). Procedure according to Claim 2 or 3rd , characterized in that the activated carbon filter (22) is modeled in the observer (60) by means of a one-dimensional model (62). Procedure according to Claim 4 , characterized in that the activated carbon filter (22) in the model (62) is divided into several parts (70), each part (70) having a gas phase (71), an adsorbent phase (72) and an adsorber wall phase (73). Procedure according to Claim 5 , characterized in that in the model (62) energy transfers (Qk) and material transfers (Ṅ _k , Ṅ _k-1 ) between the phases (71, 72, 73) are taken into account. Procedure according to Claim 5 or 6 , characterized in that in the model for each part (70) an overall molar balance of the gas phase (71), an energy balance of the gas phase (71), a loading balance of the adsorbent phase (72), an energy balance of the adsorbent phase (72), an energy balance of the adsorber wall phase (73) and a component mole balance are taken into account. Computer program, which is set up each step of the method according to one of the Claims 2 to 7 perform. Machine-readable storage medium on which a computer program Claim 8 is saved. Electronic control device (50), which is set up to use a method according to one of the Claims 2 to 7 a hydrocarbon load (Xj ^AS ) of the activated carbon filter (22) and / or a hydrocarbon stream (Ṅ _J ) through the tank ventilation line (23) of the tank ventilation system (20) Claim 1 to determine.

Images