DE10227466A1 - Determining cylinder charge in internal combustion engine, involves computing first and second cylinder charge values with first and second models, adapting first model according to comparison of results - Google Patents

Abstract

The method involves computing a first cylinder charge value (LM1) for at least one cylinder with a model (1) depending on the engine revolution rate, a choke flap angle signal and/or an induction pipe pressure signal and/or one or more valve position parameters. A second charge value (LM2) is computed with a second model (2), the computed values are compared (3) and the first model is adapted according to the comparison result. An independent claim is also included for the following: (a) an arrangement for determining a cylinder charge in an internal combustion engine.

Description

The invention relates to a method and a device for determining the cylinder load at a Internal combustion engine according to the preamble of claim 1 and claim 9, respectively.

For The control of gasoline engines is the exact knowledge of the intake Air volume required. This amount of air sucked in varies greatly the engine load. For determining the amount of air in the engine control there are different approaches. In a first approach in the prior art, the amount of air directly with a special air flow sensor or a gas sensor measured. Examples of this are a damper or a hot film air mass meter (HFM).

A disadvantage with the prior art is that when using air flow meters or Gas sensors increase costs, installation space is claimed and there is flow loss comes.

The wiring is for both sensors consuming, and there is a finite probability that they fail.

With another approach in the booth In technology, the amount of air sucked in is controlled by a so-called p-N control indirectly from the vacuum in the intake pipe and the engine speed determined, the vacuum being determined by means of an intake manifold pressure sensor becomes. However, this approach has the disadvantage that the correlation changes between intake manifold pressure and air volume with tolerances in the intake system, and this means that the air volume cannot always be determined exactly. The The result is that there are problems with compliance with strict emission limits comes. Another disadvantage is that the pressure sensor increase the cost the arrangement of the sensor is critical and the pressure sensor Weak point of the intake manifold in relation to a possible leak.

Alternatively, the amount of air in a so-called α-N system indirectly also from the measured throttle valve position and the Engine speed can be determined. However, this approach is still less precise than the previous procedure, and to adhere to sharp Emission limits practically unsuitable.

Out EP 0 820 559 A method for determining the air mass flowing into the cylinder or cylinders of an internal combustion engine is known, in which the air mass that actually flows into a cylinder is calculated by means of an intake manifold filling model that generates a load signal for the determination of a basic injection time from input variables that are determined by depend on the throttle valve opening degree and the ambient pressure as well as valve control parameters. The load signal is used for the prediction in order to estimate the load signal at a point in time that is delayed by at least one sampling process compared to a calculation of the basic injection time. The model sizes are compared in a closed control loop, using either an (HFM) sensor or an intake manifold pressure sensor. In both versions, however, the comparison of the model with the respective sensor has the sensor-specific disadvantages mentioned above with regard to installation space, probability of failure, accuracy, etc.

The object of the invention is a Specify method and to create a device with which the a cylinder of an internal combustion engine actually available Cylinder loading with the greatest possible Accuracy can be determined.

This task is solved by the method for determining the cylinder load in an internal combustion engine according to claim 1 and a corresponding device according to claim 9. Preferred embodiments the invention are the subject of the dependent claims.

The invention is based on the following consideration. The air mass sucked in by a cylinder is over a first air mass model calculated. This first air mass model can only on the sensor values of the air mass control based, e.g. the position of the throttle valve or the variable Valve lift or the variable camshaft adjustment (Vanos), or it can additionally the measured pressure in the intake pipe must also be taken into account. According to the invention, this is the first Air mass model, which describes the dynamic work area well, over a second air mass model, which is the slow or quasi-stationary work area describes well. So can individual tolerances can be compensated. The one in the second Air mass calculated model is based on the mixture composition of the Exhaust gas that over a lambda value is determined, and the fuel mass supplied.

Accordingly, a method for determining a cylinder load in an internal combustion engine is specified, in which, in an engine control, a first cylinder load value of at least one cylinder is calculated using a first cylinder load model as a function of an internal combustion engine speed and a throttle valve angle signal and / or an intake manifold pressure signal and / or one or more valve position parameters , which is characterized in that a second cylinder load value of the at least one cylinder is calculated by means of a second cylinder load model, the first cylinder load value and the second cylinder load value ver in a comparison stage are compared and a comparison signal is generated as a function of the comparison and the first cylinder loading model is adapted as a function of the comparison value.

In a preferred embodiment, the first cylinder loading model is a first air mass model with which a first air mass value is calculated as the first cylinder loading value, and the second cylinder loading model is a second air mass model with which a second air mass value is calculated as the second cylinder loading value
LM 2 = λ * x Stoich * KM,
where LM _{2 is} the second air mass value, λ is a measured air-fuel ratio, x _{stoch is} the stoichiometric air-fuel ratio and KM is a fuel _mass .

The fuel mass is preferred the fuel mass, that of a fuel mass supplied for the current cylinder loading equivalent. Alternatively, the fuel mass can also be the fuel mass be that corresponds to a predetermined target mass. In both cases the fuel mass is corrected in particular by a correction quantity be a tank ventilation mass flow corresponds, or by a correction quantity, which is an incomplete combustion of the fed Corresponds to fuel.

The first cylinder loading value is preferred through a delay device delayed by a predetermined duration before the comparator stage.

In a further preferred embodiment of the method according to the invention the first cylinder loading model is adapted depending on from the comparison value by a control stage.

The corresponding device according to the invention to determine a cylinder load in an engine control an internal combustion engine with a first cylinder loading model to calculate a first cylinder loading value of at least one Cylinders depending from an engine speed and a throttle angle signal and / or an intake manifold pressure signal and / or one or more valve position parameters is characterized by a second cylinder loading model for Calculate a second cylinder load value of the at least one Cylinder, a comparator stage for comparing the first cylinder loading value and the second cylinder load value and generating a comparison signal dependent on of the comparison and an adaptation device for adapting of the first cylinder loading model as a function of the comparison value.

An advantage of the invention is in the fact that highly accurate and therefore expensive air mass sensors such as: HFM sensors can be saved without that thereby the accuracy in determining the fresh air mass impaired becomes. The saving of the air mass sensor leads to a reduction in the Cost and at a higher Reliability. At the same time, the intake air flow is simplified and the space required is reduced, which reduces the flow losses decrease. In doing so, strict emission limit values can be observed.

Other features and advantages of Invention emerge from the following description of preferred Embodiments, reference is made to the attached drawing.

1 shows a first embodiment of the device according to the invention for determining the cylinder loading in an internal combustion engine.

2 shows a second embodiment of the device according to the invention for determining the cylinder loading in an internal combustion engine.

With the device for determining the cylinder loading in an internal combustion engine is adapted of an underlying dynamic model through a quasi-stationary model. The The invention is explained below using an air mass model.

In 1 the elements essential for the implementation of the invention are shown schematically. A first model 1 calculates a preliminary value for the air mass sucked in by one cylinder (per work cycle) based on the engine speed N and at least one other input variable. This air mass is in 1 designated LM ₁ .

In addition to the engine speed N, the input variable is in particular a variable that characterizes manipulated variables in the intake duct. These are a throttle valve angle signal α or a valve position parameter h _Einl . Another input variable is the intake manifold pressure signal p _suction. The three signals mentioned are exemplary as an input variable of the model 1 in 1 specified. In addition, signals other than those mentioned can also be used as input variables for the model 1 be used.

As known to those skilled in the art, due to the use of the model 1 determined air intake quantity of the ignition timing and other parameters for the control of the (not shown) internal combustion engine.

According to the invention by a second model 2 that regardless of model 1 is also determined a value for the air mass of a cylinder per work cycle.

This air mass is in 1 with LM ₂ be records.

The second value for the air mass is calculated according to the following basic equation:
LM 2 = λ * x Stoich * KM.

LM _{2 is} the second air mass value, λ is a measured air-fuel ratio, x _stoch is the stoichiometric air-fuel ratio, and KM is a fuel mass.

The second model depends on it exclusively from that about a (not shown) λ sensor measured air-fuel ratio and a fuel mass. The fuel mass can be a target mass for the Be fuel. This has the advantage of being the actual one Fuel mass does not need to be measured and therefore on one additional sensor can be omitted. In this case, however the real measured fuel mass corresponds to the target value.

Theoretically, the values for the air mass should be based on the first model 1 and after the second model 2 , namely LM ₁ and LM ₂ agree. Due to manufacturing tolerances can be used for the calculation of the model 1 required, measured input variables differ from their true values. This can cause discrepancies between those of the model 1 and of model 2 predicted values are coming.

The two values for the air mass sucked in by a cylinder are compared in a comparison stage 3 compared with each other. The comparison level 3 is in 1 represented symbolically by a subtractor. However, other ways of comparing two values apart from subtraction, for example by division, are also conceivable. A first input signal from the comparator stage 3 is the initial value of the model 1 , which is tapped without interrupting its output to the engine control. The second input signal of the comparator stage 3 is the initial value of the model 2 ,

Depending on the output signal of the comparator stage 3 becomes the first model 1 adapts what in 1 with an arrow through the model 1 is indicated. This is the model in a (not shown) engine control 1 adapted to real conditions so that based on the model 1 calculated control variables of the engine control - for example the injection time TI - are more precise than this without adapting the model 1 could be achieved.

The device after 1 comprises only the elements necessary for the implementation of the method according to the invention. In practice, modifications of this device are necessary so that, for example, an embodiment of the device as shown in FIG 2 is shown. Same elements as in 1 have the same reference numerals in 2 and will not be explained again.

The model value of the model 1 is slightly ahead of the model's model value due to the different input variables 2 in front. For example, the speed N is known almost immediately. In contrast, the air-fuel ratio λ is only known when the combustion has taken place in the cylinder.

In order to be able to compensate for the time difference between the first and the second model size, is in the device 2 a delay element 4 in front of the comparator facility 3 provided that the model value of the first model 1 delayed by a predetermined duration ΔT.

In addition, the comparison signal of the comparator stage must generally 3 filtered, smoothed or pre-processed in another way. This takes place in a control level 5 , The control level 5 is in 2 represented symbolically as a PI controller, but generally any controller can be used with the invention, for example also adaptive controller or neural networks. The control level 5 is used in particular to prevent the system from vibrating due to fast, counter-rotating adaptation processes.

This should have made it clear that the first model was also used in the invention 1 , which is based on dynamic input variables, serves as a basic model that is adapted as required. The second model 2 , which is based on quasi-stationary input variables such as air-fuel ratio and fuel quantity, serves to correct the basic model as required.

It must therefore be ensured that the input variables of the model 2 reflect the actual operating conditions as closely as possible. In practice, this means that in addition to the air-fuel ratio, the fuel mass used in the basic equation must also match the actual value as closely as possible. If, as described above, a target value for the fuel mass in the model 2 is used as the basis, for example, the changed fuel mass for tank ventilation, for example. In a preferred embodiment of the invention, the real metered fuel mass is increased accordingly by the loading of the tank ventilation mass flow.

Likewise, incomplete combustion of the supplied fuel must be taken into account. This particularly affects the start and warm-up of the internal combustion engine. In a further embodiment of the invention, the fuel mass is therefore reduced by a corresponding correction quantity in order to compensate for incomplete combustion of the supplied fuel, for example due to droplet formation. The following is obtained as the target fuel mass KM in the basic equation:
KM '= KM + KM 1 - KM 2 .
where KM ₁ indicates the correction regarding the tank ventilation mass flow and KM ₂ indicates the correction regarding the incomplete combustion. Although a purely additive correction of the fuel mass is specified here, the correction variables can also be multiplicative variables instead of additive variables. In any case, it results as a modified basic equation:
LM 2 = λ * x Stoich * KM ',
where LM _{2 is} again the second air mass value, λ is a measured air-fuel ratio, x _{stochi is} the stoichiometric air-fuel ratio, and KM 'is the corrected _target fuel mass.

The value for the measured air-fuel ratio λ must also Operating conditions of the internal combustion engine correspond exactly. There usually no single measurement of the air / fuel mixture per Cylinder possible the air mass is determined depending on the arrangement of the lambda sensors Bank-selective (if there is one lambda probe per bank) or all of them Across cylinders (if there is a lambda probe for all cylinders). at Multi-bank system can first of all take the individual lambda values Average and then the air mass determination over all Cylinder carried out become.

Accordingly, according to the invention one embodiment the air mass is determined in a bank-selective manner by using the measured air-fuel ratio λ at air-fuel ratio λ measured in a cylinder bank becomes. If necessary, the measured air-fuel ratio λ is an average of several, at cylinder banks measured air-fuel ratios λ used.

The air mass determination according to the model 2 is in principle not applicable in overrun cutoff mode and in secondary air mode. In these cases, however, the first air mass model 1 with those already about the model 2 determined adaptation values continue to be used to determine the cylinder air mass.

1

model 1

2

model 2

3

comparator

4

delay

5

control stage

α

Throttle angle signal

p _Spaug

Saugrohrdrucksignal

h _Einl

Inlet valve signal

Claims (12)

Method for determining a cylinder loading in an internal combustion engine, in which a first cylinder loading value (LM ₁ ) of at least one cylinder is used in an engine control system by means of a first cylinder loading model ( 1 ) is calculated as a function of an internal combustion engine speed (N) and of a throttle valve angle signal (α) and / or an intake manifold pressure signal (p _suction ) and / or one or more valve position parameters (h _Einl ), characterized in that a second cylinder _load value (LM ₂ ) of the at least one cylinder by means of a second cylinder loading model ( 2 ) is calculated, the first cylinder loading value (LM ₁ ) and the second cylinder loading value (LM ₂ ) in a comparison stage ( 3 ) are compared and a comparison signal is generated as a function of the comparison and the first cylinder loading model ( 1 ) is adapted depending on the comparison value. A method according to claim 1, characterized in that the first cylinder loading model ( 1 ) is a first air mass model with which a first air mass value (LM ₁ ) is calculated as the first cylinder load value, and the second cylinder load model ( 2 ) is a second air mass model with which a second air mass value (LM ₂ ) is calculated as the second cylinder load value according to LM 2 = λ * x Stoich * KM, where LM _{2 is} the second air mass value, λ is a measured air-fuel ratio, x _{stoch is} the stoichiometric air-fuel ratio and KM is a fuel _mass . A method according to claim 1 or 2, characterized in that the fuel mass (KM) of a fuel mass supplied for the current cylinder loading equivalent. A method according to claim 1 or 2, characterized in that the fuel mass (KM) corresponds to a predetermined target mass. A method according to claim 4, characterized in that the fuel mass (KM) is corrected by a correction quantity which corresponds to a tank ventilation mass flow (KM ₁ ). Method according to claim 4 or 5, characterized in that the fuel mass (KM) is corrected by a correction quantity which is incomplete constant combustion (KM ₂ ) of the supplied fuel corresponds. Method according to one of the preceding claims, characterized in that the first cylinder loading value (LM ₁ ) by a delay device ( 4 ) before the comparison level ( 3 ) is delayed by a predetermined duration (ΔT). Method according to one of the preceding claims, characterized in that the adaptation of the first cylinder loading model ( 1 ) depending on the comparison value by a control stage ( 5 ) he follows. Device for determining a cylinder loading in an internal combustion engine with a first cylinder loading model ( 1 ) for calculating a first cylinder loading value (LM ₁ ) of at least one cylinder as a function of an engine speed (N) and of a throttle valve angle signal (α) and / or an intake manifold pressure signal (p _Saug ) and / or one or more valve position parameters (h _Einl ) in one Engine control, characterized by a second cylinder loading model ( 2 ) for calculating a second cylinder loading value (LM ₂ ) of the at least one cylinder, a comparator stage ( 3 ) for comparing the first cylinder loading value (LM ₁ ) and the second cylinder loading value (LM ₂ ) and generating a comparison signal as a function of the comparison and an adaptation device ( 5 ) for adapting the first cylinder loading model ( 1 ) depending on the comparison value. Apparatus according to claim 9, characterized in that the first cylinder loading model ( 1 ) is a first air mass model with which a first air mass value (LM ₁ ) is calculated as the first cylinder load value, and the second cylinder load model ( 2 ) is a second air mass model with which a second air mass value (LM ₂ ) is calculated as the second cylinder load value according to LM 2 = λ * x Stoich * KM, where LM _{2 is} the second air mass value, λ is a measured air-fuel ratio, x _{stoch is} the stoichiometric air-fuel ratio and KM is a fuel _mass . Apparatus according to claim 9 or 10, characterized by a delay device ( 4 ) before the comparison level ( 3 ) to delay the first cylinder loading value (LM ₁ ) by a predetermined duration (ΔT). Device according to one of claims 9 to 11, characterized in that the adaptation device ( 5 ) is a PI controller.