DE102017209127A1 - Method for calculating a mass flow from a tank ventilation system into a suction pipe of an internal combustion engine - Google Patents

Abstract

A method is provided for calculating a mass flow of a fuel / air mixture from a tank ventilation system into an intake manifold of an internal combustion engine. In this case, a fuel / air ratio of the mass flow is taken into account in the calculation of the mass flow.

Description

The present invention relates to a method for calculating a mass flow from a tank ventilation system into a suction pipe of an internal combustion engine.

State of the art

A method for tank ventilation in the DE 10335902 B4 refer to. A tank ventilation system is in the WO 2015062793 A1 disclosed.

Disclosure of the invention

Methods are proposed for more precise calculation of a mass flow of the air-fuel mixture, which passes from a tank ventilation system in the intake manifold of the internal combustion engine. The more precise calculation, in turn, leads to a better consideration of the air components and fuel components actually introduced thereby in the calculation of control variables in the internal combustion engine by a motor controller.

Another advantage is that the tank ventilation system can be mapped and fed with just a few application factors. Especially when manufacturing variances of components such as activated carbon filter or lines (for example, in terms of cross-sections or lengths) occurring, thereby the application cost is significantly reduced.

Preferably, in the calculation of the mass flow, the fuel / air ratio over a hydrocarbon concentration and / or a viscosity of the fuel / air mixture is taken into account. In a particularly preferred embodiment, the mass flow is calculated as a function of a pressure drop across an activated carbon filter, in particular as a function of a loading of the activated carbon filter, of the tank ventilation system.

drawing

The invention is described in more detail below with reference to the accompanying drawings and to exemplary embodiments. It shows 1 schematically a section of an internal combustion engine with tank ventilation system.

Description of the embodiments

For petrol engines, the tank vent is usually controlled via the tank vent valve so that the largest possible air mass flow is passed through the activated carbon filter. The exception to this is the initial boost, where the tank vent valve is slowly turned on to allow lambda variance loading learning and to consider the fuel coming into the fuel path from the tank vent. With learned loading, it is therefore possible to control the tank venting valve further and faster and to take into account the proportion of fuel in the mixture pilot control.

1 schematically shows a section of an internal combustion engine with a tank ventilation system. In this case, fresh air passes through a suction pipe section 10 with air filter 11 to a turbocharger 12 , About a suction pipe section 13 after the turbocharger 12 with a charge air cooler 14 the air passes through a throttle valve 15 to the engine block 16 , After the engine block 16 leads a derivative 17 the exhaust off. In the suction pipe section 10 opens between air filter 11 and turbocharger 12 a first tank vent line 18 , This tank vent line 18 For example, it can only become active when an operating point of the engine with an active turbocharger occurs. It can also be called a full load line (High Load Purge Line). In the suction pipe section 13 opens between the throttle 15 and engine block 16 a second tank vent line 19 , This tank vent line, for example, is already active in the intake engine operation. It can also be referred to as a partial load line (Low Load Purge Line). The tank vent lines 18 respectively. 19 have a check valve 20 respectively. 21 , Also shown is a fuel tank 22 with a filling area 23 , About a tank ventilation section 24 An air-fuel mixture passes from the fuel tank to an activated carbon filter 25 , This one has an exit 26 to the ambient air and a derivative 27 to a tank vent valve 28 , After the tank ventilation valve 28 a tank venting section opens 29 in the first tank vent line 18 and the second tank vent line 19 ,

For the discharge point of the tank breather between throttle valve 15 and engine block 16 to the second tank vent line, the negative pressure in the intake manifold ensures the required scavenging gradient. For the discharge point to the second tank vent line 18 A venturi system ensures the purging slope of the mass flow through the tank venting valve 28 ,

For the calculation of the mass flow, via the tank ventilation ( 27 . 29 . 18 . 19 ) in the suction pipe ( 10 . 13 ), the pressure difference across the tank vent valve 28 considered. Furthermore, this mass flow depends on the duty cycle with which the tank vent valve 28 is controlled. The tank vent valve 28 is controlled via a normalized setpoint mass flow, which is converted into the duty cycle. The normalization of the mass flow is pressure-corrected, height-corrected and temperature-corrected. basics Influencing factors on the mass flow through the tank venting valve are thus, apart from the duty cycle, the pressure conditions and the density due to ambient pressure and temperature. The density of the medium, which via the tank vent valve 28 flows, but also depends on the fuel / air concentration. It is therefore proposed, for a more accurate calculation of the air-fuel mass flow through the tank ventilation system ( 27 . 29 . 18 . 19 ) in the suction pipe ( 10 . 13 ) of the internal combustion engine to correct this in dependence on a fuel / air concentration, in particular depending on a hydrocarbon concentration, a temperature, a viscosity of the mixture and the pressure conditions resulting therefrom.

This corrected mass flow is calculated in an engine control and used in particular for calculations in the air path of the engine control software and / or in the fuel path of the engine control software. Thus, for control variables of the internal combustion engine calculated in the air path, such as throttle position and control variables of the internal combustion engine calculated in the fuel path, such as injection variables, the air mass and fuel mass added from the tank ventilation are correctly taken into account. The thus calculated or corrected mass flow is thus used for a more precise control of the internal combustion engine.

In addition, proposed calculations of the mass flow are carried out in more detail.

The mass flow through the tank vent valve 28 depends on the pressure gradient between the pressure in the tank ventilation section 29 between tank vent valve 28 and the first and the second tank vent line 18 and 19 from (p to TEV) and the pressure in the tank ventilation section 27 between activated carbon filter 25 and tank vent valve 28 (p before TEV). Depending on the air mass flow through the activated carbon filter 25 and the affected line section and the loading of the activated carbon filter 25 a pressure loss occurs, which must be taken into account for the size p before TEV. P before TEV thus results from the pressure of the ambient air minus the pressure loss.

The pressure loss is determined according to the following approach: $$\Delta p=A\frac{1}{2}\rho {\dot{V}}^2+B\eta \dot{V}$$

The constants A and B depend on the geometry of the components, but not on thermodynamic quantities. According to Bernoulli, the flow pressure loss is described in the quadratic term. The linear part of the term describes the viscous pressure loss of a laminar flow in the porous medium of the filter.

ṁ: Massenstrom $$\rho =\frac{p}{RT}=\frac{pM}{ℝT}$$

$R=\frac{ℝ}{M}:$

spezifische Gaskonstante
T: Temperatur
M: Molmasse
$ℝ=\mathrm{8,3144598}\frac{\text{J}}{\text{mol }K}:$

universelle GaskonstanteThe pressure loss via optional non-return valves in the venting system (in 1 the valves 20 respectively. 21 in the first tank vent line 18 or the second tank vent line 19 ) is taken into account as a function of the mass flow and of the density of the regeneration gas and also on the viscosity.
For the mass flow, the formula is as follows: $$\Delta p=A\frac{1}{2\rho }{\dot{m}}^2+B\frac{\mu }{\rho }\dot{m}$$

ṁ: mass flow $$\rho =\frac{p}{RT}=\frac{pM}{ℝT}$$

$R=\frac{ℝ}{M}:$

specific gas constant
T: temperature
M: molecular weight
$ℝ=8.3144598\frac{\text{J}}{\text{mol}K}:$

universal gas constant

T₀, η₀, C: Konstanten aus der Literatur.The dynamic viscosity is determined by the formula of Sutherland: $$\eta ={\eta }_0\frac{T_O-C}{T-C}{\left(\frac{T}{T_O}\right)}^{\frac{3}{2}}$$

T ₀ , η ₀ , C: Constants from the literature.

• Molmasse der Komponente i: M_i
• Molmasse des Gemisches: M = ∑_ix_iM_i
• Molanteil der Komponente i: x_i
• Massenanteil der Komponente i: $w_i=\frac{x_i{M}_i}{M}$
  
• Spezifische Gaskonstante der Komponente i: $R_i=\frac{ℝ}{M_i}$
  
• Spezifische Gaskonstante des Gemisches: $R=\frac{ℝ}{M}$
  

The molar mass for the mixture flowing through the tank venting valve 28 is determined from the respective individual components:

• Molar mass of component i: M _i
• Molar mass of the mixture: M = Σ _i x _i M _i
• Molar fraction of component i: x _i
• Mass fraction of component i: $w_i=\frac{x_i{M}_i}{M}$
  
• Specific gas constant of component i: $R_i=\frac{ℝ}{M_i}$
  
• Specific gas constant of the mixture: $R=\frac{ℝ}{M}$
  

The correction factor for the viscosity is determined according to the following approach: $$\eta \left(T\right)={\displaystyle \underset{i}{\Sigma }{x}_i{\eta }_i\left(T\right)}$$

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10335902 B4 [0002]
• WO 2015062793 A1 [0002]

Claims (11)

Method for calculating a mass flow of a fuel / air mixture from a tank ventilation system into a suction pipe of an internal combustion engine, characterized in that a fuel / air ratio of the mass flow is taken into account in the calculation of the mass flow. Method according to Claim 1 , characterized in that in the calculation of the mass flow, the fuel / air ratio over a hydrocarbon concentration and / or a viscosity of the fuel / air mixture is taken into account. Method according to one of the preceding claims, characterized in that the mass flow is calculated as a function of a pressure gradient via a tank ventilation valve of the tank ventilation system. Method according to one of the preceding claims, characterized in that the mass flow is calculated depending on a temperature. Method according to one of the preceding claims, characterized in that the mass flow is calculated depending on a pressure drop over an activated carbon filter, in particular depending on a load of the activated carbon filter, the tank ventilation system. Method according to Claim 5 , characterized in that the mass flow is calculated depending on a pressure drop of a check valve in a tank vent line between a tank vent valve of the tank venting system and the intake manifold of the internal combustion engine. Method according to Claim 6 , characterized in that the mass flow is calculated in an engine control of the internal combustion engine. Method according to one of the preceding claims, characterized in that the calculated mass flow is used for a calculation of a control variable in the internal combustion engine, in particular for a calculation of a control variable of an air system of the internal combustion engine or an injection system of the internal combustion engine. Computer program, which is adapted to a method according to one of Claims 1 to 8th perform. Machine-readable storage on which a computer program is based Claim 9 is stored. Engine control unit for an internal combustion engine with a memory after Claim 10 ,

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