EP1264227A1

EP1264227A1 - Method and device for mass flow determination via a control valve and for determining a modeled induction pipe pressure

Info

Publication number: EP1264227A1
Application number: EP01913510A
Authority: EP
Inventors: Leonhard Milos; Ernst Wild; Jochen Gross; Oliver Schlesiger; Kristina Eberle; Roland Herynek; Patrick Janin; Manfred Pfitz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-02-09
Filing date: 2001-01-18
Publication date: 2002-12-11
Also published as: WO2001059536A1; JP2003522888A; CN1416541A; US20030075158A1

Abstract

A characteristic flow rate of a valve is adapted by weighing the input value valve position with a variable offset value in order to improve the accuracy of mass flow determination even when the valve is choked. The aim of the invention is to calculate a robust model for the induction pipe pressure (psaugm) by determining a modeled partial pressure (pagr) of the returned exhaust gas that deviates as little as possible from the real partial pressure of the returned exhaust gas. To this end, a modeled partial pressure (pagr) of the returned exhaust gas is derived from a characteristic flow rate of a valve disposed in an exhaust gas return pipe, depending on the valve position. The modeled partial pressure (pagr) of the returned exhaust gas derived from the characteristic flow rate is corrected adaptively, on the basis of the difference ( DELTA ps) between the modeled induction pipe pressure (psaugm) and a measured induction pipe pressure (psaug) (19).

Description

Method and device for determining a mass flow via a control valve and for determining a modeled intake manifold pressure

State of the art

The present invention relates to a method and a device for determining a mass flow via a control valve and for determining a modeled intake manifold pressure in an internal combustion engine with exhaust gas recirculation, the sum being formed from the partial pressure of the fresh gas and the partial pressure of the recirculated exhaust gas.

In many applications in the field of vehicle control, knowledge of the mass flow via a control valve is essential. An example of this is the determination of the partial pressure, for which the precise knowledge of the mass flow via an exhaust gas recirculation control valve is important. However, since the relationship between valve position and mass flow in control valves changes over time due to various factors such as aging, contamination, etc., there is a need to adapt this relationship in order to improve the accuracy of the mass flow determination, particularly in the case of valve contamination. It is known, for example from DE 197 56 919 AI, that the intake manifold pressure is calculated from the sum of the fresh gas partial pressure and the partial pressure of the recirculated exhaust gas.

An external exhaust gas recirculation system is particularly necessary for Otto engines with gasoline direct injection in order to comply with the legally required limit values for NOx emissions in the exhaust gas. Increased raw NOx emissions in the exhaust gas occur predominantly in stratified engine operation with an air / fuel ratio λ> 1. The exhaust gas recirculation, in which an exhaust gas mass flow is removed from the exhaust system and fed back to the internal combustion engine in metered quantities via an exhaust gas recirculation valve, reduces the peak temperature of the combustion process and thus reduces the raw NOx emission.

The partial pressure of the recirculated exhaust gas cannot be measured in the exhaust gas recirculation line. Therefore, only a model of the recirculated exhaust gas can be determined. In order to be able to implement a robust intake manifold pressure model which is as error-free as possible and which depends on the partial pressure of the recirculated exhaust gas, it is crucial to form a model for the partial pressure of the recirculated exhaust gas which is as free from errors as possible.

Advantages of the invention

The stated object is achieved with the features of the independent claims.

The valve flow characteristic, from which the mass flow over the valve is determined as a function of the valve position, is adapted to improve accuracy by means of an offset value which is related to the valve position of the valve. This offset value is constant over the valve position with different degrees of contamination of the valve. With an offset value related to the mass flow, on the other hand, a decrease in the offset value for a certain degree of contamination can be observed as the valve opening becomes smaller.

There are particular advantages when used on a control valve for exhaust gas recirculation. However, these advantages are also achieved with other control valves, the flow rate of which is determined on the basis of a characteristic curve depending on the valve position (e.g. throttle valves, etc.).

It is advantageous that a modeled partial pressure of the recirculated exhaust gas is derived from a flow characteristic of a valve located in an exhaust gas recirculation line depending on the valve position and that the modeled partial pressure of the recirculated exhaust gas derived from the flow characteristic is adaptive, depending on the difference from the modeled intake manifold pressure and a measured intake manifold pressure is corrected.

Advantageous developments of the invention emerge from the subclaims.

It is expedient that the mass flow via the exhaust gas recirculation valve is determined as a function of the flow characteristic of the exhaust gas recirculation valve, that a relative charge in the intake manifold is then calculated from the mass flow by dividing it by the engine speed, and finally from the relative one Filling in the intake pipe the partial pressure of the recirculated exhaust gas is derived.

It is furthermore expedient to determine a relative fresh air filling in the intake manifold from the air mass flow via the throttle valve in the intake manifold by dividing the air mass flow by the engine speed and then from the relative one - H -

Fresh air filling the partial pressure of the fresh gas is derived.

drawing

The invention is explained in more detail below on the basis of an exemplary embodiment shown in the drawing. Show it:

FIG. 1 shows a schematic illustration of an internal combustion engine with exhaust gas recirculation,

FIG. 2 shows a functional diagram for calculating a modeled intake manifold pressure,

3 shows a detail from the functional diagram of FIG. 2 for adaptively adapting the flow characteristic of the exhaust gas recirculation valve and

FIG. 4 shows a flow chart for the offset correction of the flow characteristic with an offset value related to the valve position.

Description of an embodiment

FIG. 1 schematically shows an internal combustion engine 1 with an exhaust gas duct 2 and an intake manifold 3. An exhaust gas recirculation line 4 branches off from the exhaust gas duct 2 and opens into the intake manifold 3. A valve 5 is located in the exhaust gas recirculation line 4. Via this exhaust gas recirculation valve 5, the recirculated exhaust gas mass or the partial pressure pagr of the recirculated exhaust gas can be controlled. Behind the mouth of the exhaust gas recirculation line 4, a pressure sensor 6 is arranged in the intake manifold 3, which measures the intake manifold pressure psaug. Before the opening of the exhaust gas recirculation line 4 there is a throttle valve 7 with a potentiometer 8 which detects the throttle valve position wdk. In front of the throttle valve 7, an air mass sensor 9 is arranged in the intake manifold 3, which measures the air mass flow msdk via the throttle valve 7. Furthermore, are in the intake manifold 3 in front of the throttle valve 7, a pressure sensor 10, which measures the pressure pvdk in the intake manifold in front of the throttle valve, and a temperature sensor 11, which measures the intake air temperature TANS. A pressure sensor 12, which measures the exhaust gas pressure pvagr upstream of the exhaust gas recirculation valve 5, and a temperature sensor 13, which detects the temperature Tabg of the exhaust gas upstream of the exhaust gas recirculation valve 5, are arranged in the exhaust gas recirculation line 4 upstream of the exhaust gas recirculation valve.

A control unit 14 is supplied with all of the sensed quantities mentioned. These include the measured intake manifold pressure psaug, the throttle valve position wdk, the air mass flow msdk in front of the throttle valve, the pressure pvdk in front of the throttle valve, the intake air temperature Tans, the position vs the exhaust gas recirculation valve 5, the engine speed nmot detected by a sensor 15, and the exhaust gas pressure pvagr in front of the exhaust gas recirculation valve and the temperature tab of the exhaust gas in front of the exhaust gas recirculation valve. The sizes pvdk, Tabg and pvagr can also be determined by model calculations from other operating sizes of the engine. The control unit 14 determines, among other things, the partial pressure pfg of the fresh gas and the partial pressure pagr of the recirculated exhaust gas from the input variables mentioned.

As the functional diagram in FIG. 2 shows, the desired modeled intake manifold pressure psaugm arises from an additive combination 16 of the partial pressure pfg of the fresh gas and the modeled partial pressure pagr of the recirculated exhaust gas. It is described below how the control unit 14 derives the partial pressure pfg of the fresh gas and the partial pressure pagr of the recirculated exhaust gas.

To determine the partial pressure pagr of the recirculated exhaust gas, the mass flow msagr is first calculated via the exhaust gas recirculation valve according to equation (1). msagr = fkmsagι- ^■ [msnagr (vs) + msnagr o] ^■ pvagr / 1013 bRα • -273 / Tagr ■ KLAF (psaug I pvagr) (1)

In equation (1), msnagr (vs) denotes the standard mass flow through the exhaust gas recirculation valve at an exhaust gas pressure pvagr before the exhaust gas recirculation valve of 1013hPa, Tagr = 213K and psaug / pvagr <0.52. This standard mass flow msnagr corresponds to the flow characteristic of the exhaust gas recirculation valve 5, which is usually provided by the valve manufacturer and is stored in the function block 17 (see FIG. 2). This standard mass flow msnagr (vs) is therefore a variable derived from the flow characteristic as a function of the valve position vs. The flow characteristic only takes into account the function of the exhaust gas recirculation valve 5, but not flow changes due to manufacturing tolerances and aging and also not the flow properties of the exhaust gas recirculation line 4. For this reason, in the equation (1) for the mass flow msagr via the exhaust gas recirculation valve, corrective heat fkmsagr and msnagro are provided, which can be changed adaptively. The correction term msnagro takes into account an offset of the flow characteristic. KLAF is a value taken from a characteristic curve, which shows the flow velocity over the exhaust gas recirculation valve in relation to the speed of sound as a function of the pressure ratio between the pressure psaug after the exhaust gas recirculation valve and the pressure pvagr upstream of the exhaust gas recirculation valve. If psaug / pvagr <0.52 the speed of sound is set and if psaug / pvagr> 0.52 the flow speed drops below the speed of sound.

After the mass flow msagr has been calculated via the exhaust gas recirculation valve in accordance with equation (1), a conversion into a relative filling rfagr in the intake manifold takes place in function block 17 on the basis of the recirculated exhaust gas. rfagr = msagr / {nrnot - K.) (2)

The constant K depends on the cylinder stroke volume and the standard density of the air.

Finally, the partial pressure pagr is calculated according to equation (3) from the relative filling rfagr resulting from the recirculated exhaust gas in the intake manifold on the basis of the recirculated exhaust gas.

pagr = rfagr / {KFURL ^■ ftsr) (3)

The map size KFURL indicates the ratio of the effective cylinder stroke volume to the cylinder stroke volume. The size ftsr reflects the temperature ratio of 273K to the gas temperature in the combustion chamber.

In order to determine the partial pressure pfg of the fresh gas in the intake manifold, a relative fresh air charge rlfg in the intake manifold is first determined in accordance with equation (4).

rlfg = msdk l (nmot -K) (4)

The relative fresh air charge rlfg in the intake manifold can be calculated from the air mass flow msdk upstream of the throttle valve by division by the engine speed nrnot and the constant K (see equation (2)).

After the calculation of the relative fresh air filling rlfg, the partial pressure pfg of the fresh gas is derived therefrom in function block 18 according to equation (5).

pfg = rlfg / (KFURL - flsr) (5) The partial pressure pfg of the fresh gas thus arises from the division of the relative fresh air charge rlfg by the quantities KFURL and ftsr already explained in connection with equation (3).

The air mass flow msdk upstream of the throttle valve can either be measured with the sensor 9 or can be derived from other operating variables in accordance with equation (6).

msdk = msndk (wdk) ■ pvdk / 1013hPa A / 273 / Tans • KLAF (psaug I pvdk) (6)

The msndk (wdk) is the standard mass flow through the throttle valve at a pressure pvdk before the throttle valve of 1013hPA, an intake air temperature Tans = 273K and a pressure ratio before and after the throttle valve (psaug / pvdk <0.52). The KLAF value comes from a characteristic curve and provides the flow velocity over the throttle valve in relation to the speed of sound as a function of the pressure ratio psaug / pvdk at the throttle valve. If psaug / pvdk <0.52 the speed of sound is set and if psaug / pvdk> 0.52 the flow rate drops below the speed of sound.

As already mentioned above, the partial pressure pagr of the recirculated exhaust gas derived from the flow characteristic in function block 17 is subject to errors, because this throughflow characteristic of the exhaust gas recirculation valve 5 does not take into account manufacturing tolerances, flow changes due to aging and also the flow properties of the exhaust gas recirculation line 4. In order to reduce the error of the partial pressure pagr of the recirculated exhaust gas, a function block 19 is provided, in which the partial pressure pagr of the recirculated exhaust gas is corrected. The aim is that the modeled partial pressure pagr of the recirculated exhaust gas that is available after the correction is corresponds exactly to the real partial pressure in the exhaust gas recirculation line, so that the modeled intake manifold pressure psaugm resulting from the sum of the partial pressure pfg of the fresh gas and the partial pressure pagr of the recirculated exhaust gas is as unadulterated as possible. For error correction of the partial pressure pagr of the recirculated exhaust gas, a correction variable Δps is formed by forming the difference 20 from the modeled intake manifold pressure psaugm and the intake manifold pressure psaug measured by the pressure sensor 6, which is fed to a function block 19.

As shown in FIG. 3, the correction variable Δps is fed via a switch 21 to either an integrator 22 or an integrator 23. The integrator 22 provides the correction term fkmsagr occurring in equation (1), and the integrator 23 provides the offset correction term msnagro. The integrators 22 and 23 increase the correction terms fkmsagr and msnagro to the extent that the correction variable Δps specifies. Using the correction terms fkmsagr and msnagro, the partial pressure pagr of the recirculated exhaust gas is thus adaptively changed in function block 20 until the deviation between the measured intake manifold pressure psaug and the modeled intake manifold pressure psaugm becomes minimal. A threshold value decision takes place in switching block 21, which determines whether the measured intake manifold pressure psaug exceeds the threshold of 400 hPa. At a measured intake manifold pressure psaug that lies above the threshold of 400 hPa, only the integrator 23 for the correction term msnagro is controlled by the correction variable Δps. If the measured intake manifold pressure psaug is below the threshold of 400hPa, the correction variable Δps is switched over to the integrator 22 for the correction term fkmsagr.

The mass flow via the valve is required to determine the partial pressure. This is based on an adap- animal characteristic is determined depending on the valve position. Such a characteristic curve can also be essential in connection with other applications, so that the characteristic curve adaptation described cannot only be used in exhaust gas recirculation. For example, the air mass flow via a throttle valve is also determined in accordance with a flow characteristic, which can also be changed by valve contamination. As shown in FIG. 3, the offset value is formed from the deviation of a value calculated using the characteristic curve with a measured value, for example by integration.

FIG. 4 shows a flow chart for the adaptation of such a flow characteristic. The input variable is the valve position vp. With this, the determined offset value off (in the exemplary embodiment of an EGR valve ofvpagr, see e.g. FIG. 3, offset value msnagro) is linked (added) in the linkage point 25. The result is used to address the flow characteristic MSNTAG 26, the output variable of which is the standard mass flow msnv (in the exemplary embodiment of an EGR valve msnagrv) via the control valve, which if necessary by linking 27 (division) with a slope adaptation factor to the standard mass flow msn (in the exemplary embodiment of an EGR - valve msnagr) is linked.

In the above exemplary embodiment of a partial pressure determination using the flow characteristic over an EGR valve, the offset value is related to the mass flow as described in equation 1. It is cheaper to refer to the valve position here as well. The following calculation equation for the mass flow then results:

msagr = 1 / fkmsagr ^■ [msnagr] - pvagr / 1013hPa ^■ ^ 273 / Tagr

^■ KLAF (psaug I pvagr) (7) This equation represents the physically correct behavior of the mass flow via the EGR valve depending on the contamination of the valve. In contrast to equation (1), the offset can no longer be recognized. It is evaluated when addressing the flow characteristic curve, the output signal of which is the quantity msnagr (mass flow under standard conditions). The output value is therefore not adapted, rather the input value of the characteristic curve, that is to say the valve position, is adapted by the offset.

Claims

Expectations

1. Method for determining a mass flow via a control valve,

- whose position is recorded,

the mass flow is determined according to a characteristic curve depending on the position,

- The characteristic curve being adapted with a variable offset value, characterized in that

- The valve position is corrected with the offset value and the mass flow is determined from the characteristic curve depending on the corrected valve position.

2. The method according to claim 1, characterized in that the offset value is derived from the deviation of a variable calculated on the basis of the mass flow and the measured variable.

3. A method for determining a modeled intake manifold pressure in an internal combustion engine with exhaust gas recirculation, the sum of the partial pressure (pfg) of the fresh gas and the partial pressure (pagr) of the recirculated exhaust gas being formed, characterized in that a modeled partial pressure (pagr) of the recirculated exhaust gas from a flow characteristic of a valve (5) located in an exhaust gas recirculation line (4) as a function of the valve position lung (vs) and that the modeled partial pressure (pagr) of the recirculated exhaust gas derived from the flow characteristic curve is adaptively corrected as a function of the difference (Δps) from the modeled intake manifold pressure (psaugm) and a measured intake manifold pressure (psaug) (20) becomes.

4. The method according to claim 3, characterized in that the mass flow through the exhaust gas recirculation valve (5) in dependence on the flow characteristic of the exhaust gas recirculation valve

(5) it is determined that from the mass flow, by dividing it by the engine speed (nmot), a relative filling in the suction pipe (3) is calculated and that the partial pressure (pagr) of the recirculated from the relative filling in the suction pipe (3) Exhaust gas is derived.

5. The method according to claim 3, characterized in that from the air mass flow (msdk) via the throttle valve (7) in the intake manifold (3) a relative fresh air filling in the intake manifold (3) is determined by the air mass flow (msdk) by the engine speed (nmot ) is divided, and that the partial pressure (pfg) of the fresh gas is derived from the relative fresh air filling.

6.Device for determining a mass flow via a control valve, with a control unit which detects the position of the control valve, which determines the mass flow according to a characteristic curve depending on the position, and which adapts the characteristic curve with a variable offset value, characterized in that the Control unit has means that correct the valve position with the offset value and determine the mass flow from the characteristic curve depending on the corrected valve position.

7. Device for determining a modeled intake pipe pressure in an internal combustion engine with exhaust gas recirculation. which forms the sum of the partial pressure (pfg) of the fresh gas and the partial pressure (pagr) of the recirculated exhaust gas, characterized in that means (17) are present which generate a modeled partial pressure (pagr) of the recirculated exhaust gas from a flow characteristic of one in a Derive exhaust gas recirculation line (4) located valve (5) depending on the valve position (vs) and that further means (19) are provided, which adaptively from the modeled partial pressure (pagr) of the recirculated exhaust gas derived from the flow characteristic, depending on the difference (Δps) from the modeled intake manifold pressure (psaug) and a measured intake manifold pressure (psaug).