DE10222808A1 - Air-fuel ratio control method for an internal combustion engine determines composition of total mass of recycled ventilation gas in positive crankcase ventilation. - Google Patents

Abstract

During every engine operating state, a composition of the total mass (mPCV) of a ventilation gas recycled via a positive crankcase ventilation (PCV) valve is determined in a control device (CD) via exhaust gas values detected, operating values of fuel supplied, combustion air and engine oil temperature and taken into account in the CD in order to adjust air-fuel ratio fed to the engine.

Description

The invention relates to a method for regulating the air / fuel ratio for an internal combustion engine with those mentioned in the preamble of claim 1 Features.

From DE 100 36 128 A1 an internal combustion engine and a Process for active ventilation of a cylinder crankcase (PCV = positive Crankcase ventilation). There is an intake tract of the engine for fresh air above one Bypass with the channel of the active ventilation of the cylinder crankcase connected. The cylinder crankcase is over an oil separator, one downstream PCV valve connected to the intake manifold of the engine via a duct. the Intake manifold are the oil-laden air extracted from the cylinder crankcase and blowby gases and also recirculated exhaust gas are fed to the intake tract.

It is previously known in PCV systems for the regulation of the motor Air / fuel ratio, to consider the fuel as a homogeneous medium, whereby a simple counter function per piston stroke is used for the entry. With great simplification of motor dependencies such as blowby mass and Engine temperatures become an estimate of the fuel output from the lubricating oil determined and this from an entry determined with the same inaccuracy and one resulting amount of memory deducted. The fuel discharge amount leads to Reduction of the injection quantity for the following combustion. The PCV Mass gas flow is also regarded as homogeneous and compromised its composition equated to air, although it is next to the Fuel vapors also contain blowby gases. The influence of the change in air mass will application compensated, that is, the increased air mass flow is in the Engine control unit calculation included. The engine oil temperature is either over the WIV function (maintenance interval extension) detected by the corresponding sensor or modeled in a highly abstract manner.

By adopting the fuel as a homogeneous medium, considerable Temperature dependencies of the evaporable fuel components are not exact be modeled and lead to great inaccuracies in the Injection mass calculation. The additive air correction contains no information about the composition of the PCV gas mass flow, which is primarily for engines with a high blowby component leads to significant errors in the air mass calculation. The modeling of the Oil temperature is highly imprecise and does not guarantee reproducibility Results.

DE 198 14 667 A1 describes an air / fuel ratio control system for a Internal combustion engine taking into account the ventilation of the fuel tank previously known. The intake tract of the internal combustion engine is the Venting device of the fuel tank connected and comprises at least one Fuel injection valve that injects fuel into the internal combustion engine. The air / fuel ratio Control system has one between the fuel tank and the internal combustion engine arranged adsorption unit, which a fuel vapor generated in the fuel tank Emission gas adsorbed. Is between the adsorption unit and the internal combustion engine a suction system and a vent valve arranged by the control unit adjustably controls a flow rate of the gas adsorbed in the adsorption unit in order to To vent gas to the internal combustion engine.

The control system consists of a first calculation device, the one amount of fuel to be injected in accordance with an operating condition of the Internal combustion engine calculated, further from a determination device, the one permissible fuel quantity determined and a second calculation device, the a quantity of the gas to be vented from the adsorption unit Calculated according to the actual fuel injection quantity.

In this air / fuel ratio control system, only the one from the Returned fuel quantity taken into account in fuel tank ventilation. Active ventilation of the cylinder crankcase and thus a consideration of this There is no correlation between returned oil-laden gases and the blowby gases intended.

The invention has for its object a method for controlling the Air / fuel ratio for an internal combustion engine with an active to create ventilated cylinder crankcase, depending on which from the Cylinder crankcase recirculated oil-laden gases and the blowby gases the fuel and air quantities actually required during engine operation are set and the returned PCV mass flow qualitatively and quantitatively can be assessed.

This object is achieved by the characterizing features of Claim 1 solved.

The fact that during the respective operating state of the engine on the recorded exhaust gas values, the operating values of the fuel supplied, the Combustion air and the engine oil temperature in the control unit the occurring Composition of the total mass of vent gas returned via the PCV valve is determined and in the control unit for setting the supplied to the engine Air / fuel ratio is taken into account, both the recycled Fuel share as well as the combustion air share of the total PCV mass in the control of the air / fuel ratio supplied to the internal combustion engine. Inaccuracies in the injection mass calculation of the engine supplied The amount of fuel and combustion air are largely excluded. With of the solution according to the invention, the PCV returned to the motor Overall masses assessed and assessed qualitatively and quantitatively.

Further advantageous refinements are described in the subclaims are explained in the description together with their effects.

An exemplary embodiment of the invention is described below with the aid of a drawing described. In the accompanying drawings:

Fig. 1 is a schematic representation of a PCV-motor,

Fig. 2: a representation of the Siedekennlinien of Otto fuels,

Table 1: a list of the masses occurring on the PCV engine,

Table 2: a list of the existing dependencies,

Table 3: a list of the fuel mass flow calculation,

Table 4: a list of the air mass flow calculation,

Table 5: a model principle of PCV adaptation via lambda,

Table 6: a list of other functions.

The content of the invention is a method that runs in the engine control unit and that at any time the current composition of the sucked charge and its air and Determines fuel proportions and an adjusted injection quantity accordingly calculated.

• - das Siede- und Kondensationsverhalten des Kraftstoffes wird in mindestens 2, besser mehr Temperaturbereiche aufgeteilt, um den weiten Siedebereich der Kraftstoffkomponenten hinreichend genau darzustellen (siehe Fig. 2),
• - der Erwärmungs-, Brenn- und Alterungsvorgang eines Verbrennungsmotors,
• - den Anteil an Inertgas des Blowby-Gases,
• - Verwendung des Öltemperatursignals aus der Ermittlung des Ölwechselintervalls,
• - weitere motoreigene Funktionen, wie beispielsweise Motorverschleiß zur Modellpräzisierung.

The following parameters are taken into account in the approach:

• the boiling and condensation behavior of the fuel is divided into at least 2, better more temperature ranges in order to represent the wide boiling range of the fuel components with sufficient accuracy (see FIG. 2),
• - the heating, burning and aging process of an internal combustion engine,
• - the proportion of inert gas in the blowby gas,
• Use of the oil temperature signal from the determination of the oil change interval,
• - Other engine-specific functions, such as engine wear for model precision.

Fuel path - according to table 3

In the warm-up phase of an internal combustion engine, its thermal increases Degree of implementation many times faster than the engine oil temperature.

The engine oil temperature is decisive for the evaporation of the entered Responsible for fuel.

Below a threshold value of the heat supplied to the combustion chamber, one can due to the leakage of pure fuel and its complete entry in run out of oil. This is weighted with a warm-up factor F_WL.

With increasing temperature, the mixture preparation improves, whereby the low-boiling components mostly remain in the combustion chamber and only the high-boiling ones get into the oil. Therefore F_WL for the n Temperature ranges are filed.

If no heat is supplied, that means the starter turns the engine without incipient combustion (starting problems), the fuel input with a Start factor weighted (F_ST) possibly also depending on the Starting temperature.

Above the heat threshold, the fuel input is only that fuel-air mixture set, since more fuel mass in the intake and compression tract is available. This is done with a mixture factor F_G compensated. From the above For reasons it is also filed n times.

All the effects just mentioned are inseparable from the engine start temperature coupled and are shown accordingly in function of this.

As soon as the first portions of fuel heat up during engine oil heating Reach boiling temperature, they begin to evaporate.

A fuel vapor mist is formed, which is torn in the direction of the intake manifold by the system's own ventilation mass flow (mPCV). ( Fig. 1)

• - Anteil nichtkondensierter KS aus Blowby F_BB,
• - Verdampfungspotential aus akkumulierten Kraftstoffmassen in n Klassen F_m_n (je mehr Masse eingetragen wurde, um so mehr kann ausdampfen),
• - Destillationsbestreben der n Kraftstoffe bei T_Öl (je größer T_Öl, desto stärker dampfen leicht siedende Anteile aus, während schwersiedende noch im Öl verbleiben und erst bei höheren Temperaturbereichen ausdampfen)
• - maximales Kraftstoff/Luft-Verhältnis (Sättigungsverhältnis) im PCV-Gas in Abhängigkeit von der Saugrohrtemperatur F_FA (Saugrohr ist kältester Teil auf dem Weg des Kraftstoffes zum Brennraum, und dieser wird deshalb dort auch schon zum Teil kondensieren).

The fuel content of this mass flow depends on its relative saturation and cannot exceed the absolute saturation (mKS_PCV_max). The saturation factor F_S is made up of:

• - proportion of uncondensed KS from Blowby F_BB,
• Evaporation potential from accumulated fuel masses in n classes F_m_n (the more mass entered, the more can evaporate),
• - Distillation efforts of the n fuels at T_Öl (the larger T_Öl, the more low-boiling components evaporate, while high-boiling components still remain in the oil and only evaporate at higher temperature ranges)
• - Maximum fuel / air ratio (saturation ratio) in the PCV gas as a function of the intake manifold temperature F_FA (intake manifold is the coldest part on the way of the fuel to the combustion chamber, and this will therefore already partially condense there).

Air path - according to table 4

The ventilation mass supplied to the intake manifold via the PCV system is via a throttle of a pneumatic valve is regulated depending on the intake manifold pressure and the fresh air flow is limited. This makes this total gas mass overall Operating range (speed, load, temperature) defined, reproducible and therefore to be regarded as constant for each individual operating point.

This gas mass is stored in a corresponding model.

The PCV gas mass is composed of air (ventilation or Ventilation air), blowby and fuel mass.

The blow-by mass initially decreases during the runtime (run-in effect). at increased wear (increased mileage) it rises over the new condition.

The composition of the blowby from fresh air and from combustion Originating inert gases depend on the operating point and wear pattern.

If the blowby proportion increases while the PCV mass remains the same (see above) the proportion of ventilation decreases accordingly, so that comes from the blowby Inert gas share of the PCV mass flow depending on mileage and Operating condition. This relationship is related to the blowby factor over mileage (F_LL) and the fresh air percentage is increased or reduced accordingly.

Model comparison using lambda control - according to Table 5

By precisely modeling the effects of a PCV system on fuel and air path, it is possible to detect any mixture deviations in the exhaust gas (which is detected by the lambda probe and fed to the control unit as a value is) better the individual elements of the motor periphery and thus also that Allocate PCV system.

As long as the injection mass calculated from the intake air mass measured lambda in the exhaust gas is neither a fuel input nor - determine discharge. The calculated and supplied fuel masses remain unchanged.

If the ACTUAL_Lambda falls significantly below the target value, it will assumed that the mixture enrichment in the exhaust gas from evaporated fuels comes from the oil. It is checked whether the engine oil is above the lowest Temperature range limiting temperature T1 is. If that is not the case can be assumed that no KS evaporation process has started. A KS flow via the PCV can thus be excluded and the error must be assigned to another system. The calculated n Fuel masses remain unchanged.

However, if the oil temperature is above the first threshold, it is checked whether it also exceeds the second. If this is not the case, the Lambda set and the calculated fresh air mass one Fuel mass difference determined. This amount corresponds to the PCV-KS mass flow and is in written a memory. At the same time, the injection mass of the subsequent combustion and the accumulated mass of the lowest temperature range reduced by their amount. In the next calculation cycle, the memory updated.

The same applies to all n subsequent temperature ranges.

However, depending on the oil temperature and the point below Saturation criteria called fuel path a weighting of the mass fractions performed. These in turn serve to update the memory and are selectively subtracted from the corresponding temperature ranges.

If the target / actual lambda comparison shows a mixture that is too lean in the exhaust gas, then the injected fuel is not optimally enforced. It will assumed that the missing fuel mass leading to the mixture leaning over the annular gap between the piston and the cylinder wall enters the crankcase is. It is checked whether the temperature of the engine oil is above the lowest Temperature range limiting temperature T1 is. If that is not the case can be assumed that no fuel Evaporation process has started. Thus, a fuel flow over the PCV will be excluded and the total fuel error mass will be on the n Temperature ranges evenly distributed. There is an increase in corresponding storage values, accumulated masses and the injection time.

However, if the oil temperature is above the first threshold, it is checked whether it also exceeds the second. If this is not the case, the fuel Error mass on the remaining n-1 temperature ranges according to the Oil temperature and as an inversion of the one mentioned under the point fuel path Evaporation efforts weighted and distributed.

The same applies to all n subsequent temperature ranges.

However, the engine oil temperature is above the highest temperature range limiting threshold, the error must be assigned to another system become.

Other functions - according to table 6

The fuel input and output is dependent on the vapor pressure. The lower the Vapor pressure, the less fuel remains in gaseous form in the combustion chamber. This testifies increases fuel input, lower vapor pressure and otherwise around. About the one described in the model adjustment using lambda control Function, this deviation is determined and z. B. the Starting injection quantity correction provided.

Furthermore, the fuel input is clearly from the blowby and thus that Depends on engine wear. Thus, the averaged fuel input over the runtime compared to a reference value. From this one can make a statement about increased or reduced engine wear.

Under certain boundary conditions such as wear condition, temperature, and Speed it is possible that at full load in the crankcase due to increased Blowby builds up an overpressure that propagates into the intake manifold. With that the measured intake manifold pressure is greater than the ambient pressure and leads to Falsification of the ambient pressure calculation.

Depending on the wear mentioned above, a corresponding reduction.

Table 1 masses

m

_air

^exhaust

: stoichiometric air mass in the exhaust gas

m

_air

^Suction

: total air mass sucked in

m

_air

^PCV

: Air mass sucked in via the PCV system

m

_air

^ventilation

: PCV fresh purging air

m

_KS

^inj

: injected fuel mass

m

_KS

^exhaust

: stoichiometric fuel mass in the exhaust gas

m

_KS

^bypass

: fuel mass flowing away through wall mounting

m

_KS

^oil

: Fuel mass in the oil

m

_KS

^PCV

: Fuel mass from the oil

m

_blowby

: Blowby mass (inert gas, HC, water and fresh air)

m

_PCV

: Total PCV mass

Table 2 dependencies

m

_air

^exhaust

= m

_air

^Suction

 - ƒ

_air

(m

_blowby

)

m

_air

^Suction

 = ƒ (p

_atm

; p

_Suction

; n; t

_air

; m

_air

^PCV

)

m

_air

^PCV

 = m

_air

^ventilation

 + ƒ

_air

(m

_blowby

)

m

_air

^ventilation

 = ƒ (p

_atm

; p

_KK

; p

_Suction

; n; t

_air

)

m

_KS

^inj

 = m

_air

^Suction

/ λ / A / F ratio - m

_KS

^PCV

m

_KS

^exhaust

 = m

_KS

^inj

 + m

_KS

^PCV

 - m

_KS

^bypass

 - ƒ

_KS

(m

_blowby

)

m

_KS

^bypass

 = ƒ (p

_Suction

; n; t

_mot

; t

_oil

; km-LL)

m

_KS

^oil

 = m

_KS

^oil

 + m

_KS

^bypass

 + ƒ

_KS

(m

_blowby

) - m

_KS

^PCV

m

_KS

^PCV

 = ƒ (m

_PCV

; m

_KS

^oil

; t

_oil

; t

_air

)

m

_blowby

 = ƒ (p

_Suction

; p

_KK

; n; t

_mot

; t

_oil

; km-LL)

m

_PCV

 = (m

_air

^ventilation

 + m

_blowby

 + m

_KS

^PCV

)

Table 6 More functions

Fuel detection

there m

_KS

^bypass

 and m

_KS

^PCV

 depending on the KS vapor pressure

Blow / wear recognition

there m

_KS

^oil

 and m

_KS

^PCV

 depending on the m

_blowby

Correction of atmospheric pressure

Since p

_Suction

 at full load depending on m

_blowby

 (old engine)

Claims (10)

1. Method for regulating the air / fuel ratio for an internal combustion engine, which has the following structure:
an active cylinder crankcase ventilation, which is connected to the outside air via a bypass and is connected to the intake tract via a separating element, a duct and a PCV valve,
a control system which, in accordance with an operating state of the internal combustion engine, calculates an amount of fuel which is to be injected into the intake tract or cylinder by fuel injection valves and calculates an amount of air which is supplied to the engine and which is regulated by a throttle valve and is supplied to the engine via the intake tract,
a lambda probe connected to the control system, characterized in that during the respective operating state of the engine, the composition of the total mass of the venting gas which is returned via the PCV valve is determined via the detected exhaust gas values, the operating values of the supplied fuel, the combustion air and the engine oil temperature in the control unit and is taken into account in the control unit for setting the air / fuel ratio supplied to the engine. 2. The method according to claim 1, characterized, that the returned fraction fractions of the fuel in the vent gas from the Temperature of the oil and depending on the previously determined entry of Fractions of the fuel in the oil can be determined. 3. The method according to one or more of the preceding claims, characterized, that the recycled fraction fractions of the fuel and the proportion of inert gas in blowby gas depending on the heating, burning and Aging process of the engine can be determined. 4. The method according to one or more of the preceding claims, characterized, that for several temperature ranges of the oil or fuel Warm-up factor for the boiling and distillation behavior of the fuel in the storage tank the control unit is stored and readable. 5. The method according to one or more of the preceding claims, characterized, that a stored start factor is taken into account when starting the engine and is read out. 6. The method according to one or more of the preceding claims, characterized, that above a threshold engine temperature, the fuel input with one for the respective engine temperature or for the respective one Engine temperature range stored mixture factor is corrected. 7. The method according to one or more of the preceding claims, characterized in that the fuel content in which the engine determines the total mass of vent gas returned by the PCV valve, taking into account a saturation factor, which depends on
the proportion of uncondensed blowby fuel,
the fuel masses entered in the oil as well as their boiling and evaporation behavior in specified temperature ranges,
the respective oil and intake manifold temperature
is formed. 8. The method according to one or more of the preceding claims, characterized in that
a value is stored in the memory of the control device which is constant for each operating point and characterizes the air mass returned via the PCV valve,
a value for the returned air mass is corrected in the control unit as a function of the running time, the wear pattern and the respective operating point of the engine,
and the air masses supplied to the engine are set by means of the values determined in the control unit. 9. The method according to one or more of the preceding claims, characterized, that via the lambda control that via the PCV valve depending on the Engine oil temperature returned fuel mass according to its boiling and Evaporation behavior determined in the respective temperature range and in the Total amount of fuel to be supplied to the engine is taken into account. 10. The method according to one or more of the preceding claims, characterized, that the setting of the air / fuel ratio supplied to the engine in Dependence of the vapor pressure of the fuel, the engine wear and the corrected atmospheric pressure.