DE102016206491A1 - A method and apparatus for operating an internal combustion engine with a VCR controller and for verifying a function of a VCR controller - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (2) with a VCR actuator (6) for setting a compression ratio in a cylinder (3) of the internal combustion engine (2), in particular based on an indication of an actual compression ratio (εEst), with the following Steps: determining a modeled actual engine torque (MMdl), a modeled compression efficiency (ηMdl) and an actual actual engine torque (MEst); Determining an actual compression efficiency (ηEst) based on a moment balance; and - determining the actual compression ratio (εEst) depending on the actual compression efficiency (ηEst).

Description

Technical area

The invention relates to internal combustion engines, in particular reciprocating internal combustion engines, with VCR (Variable Compression Ratio VCR), which allow a variable adjustment of a compression ratio of combustion chambers of the internal combustion engine. Furthermore, the invention relates to methods for operating an internal combustion engine with a VCR actuator, in particular for checking a function of a VCR actuator.

Technical background

For reciprocating internal combustion engines, it is possible to set a compression ratio in the combustion chambers of the cylinder by various measures. The compression ratio indicates a ratio between a maximum volume of the combustion chamber and a minimum volume of the combustion chamber during a power stroke of the internal combustion engine. The compression ratio can be adjusted variably by suitable so-called VCR controller by specifying a VCR control variable.

For example, from the document WO 2014/019684 a reciprocating internal combustion engine with variable compression and with an operating unit for changing a compression ratio known. The actuator unit has a variable length connecting rod, a variable compression height piston, and / or a crankshaft with a variable crankshaft radius.

Furthermore, from the document DE 10 2008 050 827 A1 an adjusting device for a crankshaft of an internal combustion engine known. The crankshaft is mounted in adjusting bearings which are adjustable via an adjusting shaft to change the position of the crankshaft between a minimum compression position and a maximum compression position of a piston in a cylinder.

From the publication US 2014/0014071 Furthermore, an apparatus for adjusting a variable compression ratio in an internal combustion engine is known. The device comprises an eccentric bearing device for receiving the crankshaft. The eccentric bearing device comprises a rotatable eccentric ring, in which the crankshaft is mounted, wherein the compression ratio can be adjusted by rotating the eccentric ring.

Disclosure of the invention

According to the invention, a method for operating an internal combustion engine with a VCR actuator according to claim 1, a method for checking a function of a VCR actuator in an internal combustion engine, an apparatus and an engine system with an internal combustion engine according to the independent claims are provided.

Further embodiments are specified in the dependent claims.

• – Bestimmen eines modellierten Ist-Motormoments, eines modellierten Kompressionswirkungsgrads und eines tatsächlichen Ist-Motormoments;
• – Bestimmen eines tatsächlichen Kompressionswirkungsgrads basierend auf einer Momentenbilanz; und
• – Ermitteln eines tatsächlichen Verdichtungsverhältnisses abhängig von dem tatsächlichen Kompressionswirkungsgrad.

According to a first aspect, there is provided a method of operating an internal combustion engine with a VCR actuator for adjusting a compression ratio in a cylinder of the internal combustion engine, in particular based on the actual compression ratio. The method comprises the following steps:

• Determining a modeled actual engine torque, a modeled compression efficiency, and an actual actual engine torque;
• Determining an actual compression efficiency based on a moment balance; and
• - Determining an actual compression ratio depending on the actual compression efficiency.

Combustion engines with VCR controllers allow a reduction in fuel consumption by optimizing the charge cycle losses by adjusting a compression ratio in the combustion chambers of the cylinders. Since the thermal efficiency of an internal combustion engine depends on the compression ratio, a suitable compression ratio can be set operating point-dependent for the operation of internal combustion engines. In particular, at low and part load operating points, high thermodynamic efficiency can be achieved through a high compression ratio, while at high load operating points the compression ratio is reduced to reduce knock tendency of the internal combustion engine.

In order to obtain the greatest possible degree of efficiency with regard to the mechanical energy obtained, the compression ratio during normal operation, ie in normal operation, is usually selected as high as possible, ie close to the knock limit (operating range limit from which knocking of the internal combustion engine occurs). In a Aufheizbetriebsart in which the internal combustion engine is operated so that the catalyst in the Abgasabführungsabschnitt is preferably heated to an operating temperature, there is a goal, however, in the implementation of the fuel energy as possible provide high proportion of exhaust energy for heating the catalyst. Therefore, it is usually provided to operate the internal combustion engine during the Aufheizbetriebsart with a higher engine load and to delay the ignition timing to achieve increased thermal energy input into the exhaust system for rapid heating of the catalyst. Under certain circumstances, this effect is exacerbated when the engine speed is increased.

The compression ratio can be adjusted variably by means of so-called VCR controllers by specifying a VCR control variable. However, a diagnosis of the positioning behavior of the VCR actuator is usually only possible with the aid of a position sensor which provides a position feedback of the VCR actuator. However, such provision of such a position sensor for a VCR actuator represents an additional expense.

The above method now provides a determination of the actual compression ratio to verify a function of a VCR actuator or an adaptation of the VCR actuator, without requiring a sensory detected position indication of a position sensor. For this purpose, the actual compression efficiency is derived from a moment balance and then determined from the compression efficiency, the actual compression ratio. The torque balance is based on an actual engine torque calculated from the torque calculation path, a compression efficiency calculated from the torque calculation path, and an actual engine torque derived from the average pressure of the combustion. By comparing the engine torques determined in various ways, an actual compression efficiency can be derived.

In addition, the effect of the respective compression ratio on the engine parameters can be taken into account. Another advantage of the above method is that it can be applied independently of the operating condition of the internal combustion engine. As a result, no special operating state of the internal combustion engine has to be set in order to carry out the diagnosis.

Furthermore, an error can be signaled if the actual compression ratio deviates from a predetermined target compression ratio, in particular by more than a predetermined tolerance value. This allows a permanent diagnosis of the VCR controller.

Also, a VCR manipulated variable for setting the VCR controller may be adapted based on the actual compression ratio. As a result, component tolerances and aging-related changes in the VCR controller can be compensated.

According to an embodiment, the VCR manipulated variable may be regulated depending on the actual compression ratio and the target compression ratio.

Furthermore, the actual actual engine torque can be determined from an indication of the cylinder center pressure, in particular depending on a stroke volume of a cylinder.

In particular, the cylinder center pressure can be determined by means of a curve of a measured cylinder pressure or by means of a profile of the rotational speed of a crankshaft of the internal combustion engine.

• – ein modelliertes Ist-Motormoment, einen modellierten Kompressionswirkungsgrad und ein tatsächliches Ist-Motormoment zu bestimmen;
• – einen tatsächlichen Kompressionswirkungsgrad basierend auf einer Momentenbilanz zu bestimmen; und
• – ein tatsächliches Verdichtungsverhältnis abhängig von dem tatsächlichen Kompressionswirkungsgrad zu bestimmen.

According to another aspect, there is provided an apparatus for operating an internal combustion engine having a VCR actuator for adjusting a compression ratio in a cylinder of the internal combustion engine, the apparatus being configured to:

• To determine a modeled actual engine torque, a modeled compression efficiency, and an actual actual engine torque;
• To determine an actual compression efficiency based on a moment balance; and
• To determine an actual compression ratio depending on the actual compression efficiency.

Furthermore, an adaptation unit may be configured to determine a VCR manipulated variable for driving the VCR actuator by means of a control depending on a difference between the actual compression ratio and a predetermined target compression ratio.

In another aspect, an engine system including an internal combustion engine and the above apparatus is provided.

Description of the drawings

Embodiments are explained below with reference to the accompanying drawings. Show it:

1 a schematic representation of an engine system with an internal combustion engine having a VCR actuator for setting a variable compression ratio in the combustion chambers of the cylinder; and

2 a flowchart illustrating a method for operating an internal combustion engine with a VCR controller; and

3 a schematic block diagram of an adaptation circuit for controlling a VCR actuator.

Description of embodiments

1 shows a schematic representation of an engine system 1 with an internal combustion engine 2 formed in the form of a reciprocating internal combustion engine. The internal combustion engine 2 may be formed for example in the form of a gasoline engine or diesel engine.

The internal combustion engine 2 has cylinders 3 on, the combustion chambers 31 in which, in a conventional manner, a piston 4 is movably arranged. The piston 4 is at his the combustion chamber 31 opposite side via a (not shown) connecting rod with a crankshaft 5 coupled, so that by a combustion cycle in the internal combustion engine 2 caused stroke movement of the piston 4 in a rotational movement of the crankshaft 5 is implemented.

The internal combustion engine 2 Otherwise, it is designed like a conventional internal combustion engine. The internal combustion engine 2 Fresh air is supplied via an air supply system 7 supplied and combustion exhaust gases from the cylinders 3 via an exhaust removal system 8th dissipated. In the exhaust system 8th can be a catalyst 9 or a comparable exhaust aftertreatment device may be arranged.

The coupling between the crankshaft 5 and the piston 4 in the cylinders 3 can with a VCR-controller 6 (VCR: Variable Compression Ratio) to provide a compression ratio in the cylinders 3 adjustable. The compression ratio corresponds to a ratio of a maximum volume of the combustion chamber 31 the cylinder 3 ie the volume of the combustion chamber 31 when the piston 4 located at a bottom dead center, to a minimum volume of the combustion chamber 31 the cylinder 3 ie a volume of the combustion chamber 31 when the piston 4 located at a top dead center. Common to all VCR writers 6 that is the position of the piston 4 changes at top dead center depending on the compression ratio to be set. In particular, the top dead center is the closer to a combustion chamber roof 16 of the combustion chamber 31 the higher the set compression ratio is.

The internal combustion engine 2 is in a conventional manner by a control unit 10 operated. In addition to the parking facilities for operating a conventional internal combustion engine 2 are provided, the control unit 10 also the VCR-Steller 6 put.

An advantage of the adjustability of the compression ratio ε results from the dependence of the thermal efficiency η _{TH of} an internal combustion engine on the compression ratio, as follows: η _TH = 1 - (1 / ε) ^κ-1

Here, ε describes the compression ratio, which is usually between 8 and 14 in gasoline engines, and κ the isentropic exponent of the mixture, which can be assumed to be about 1.3 for homogeneous combustion. Thus, the thermal efficiency η _{TH is} increased by about 10% over the entire adjustment range of the compression ratio with an increase in the compression ratio from a minimum value to a maximum value.

Thereby, the fuel consumption of the internal combustion engine can be reduced.

In normal operation, the compression ratio is substantially adjusted so that it is as large as possible, but knocking of the internal combustion engine is avoided. This means that at high load operating points and partial load operating points, a high and a maximum compression ratio is set, while in high load operating points, the compression ratio is reduced accordingly, so that no knocking occurs in the internal combustion engine.

The VCR controller 6 is usually set with the aid of a VCR manipulated variable. Some VCR systems have a position sensor to indicate the actual position of the VCR controller 6 to check. However, the provision of such a position sensor is expensive, and it is therefore desirable to provide other ways to check whether a desired position of the VCR actuator 6 also corresponds to an actual position.

In 2 FIG. 3 is a flow chart illustrating a method of checking a function of a VCR controller. Overall, the method provides, with the aid of a torque balance, a calculated actual engine torque M _Mdl and a calculated compression efficiency equal to an actual actual engine torque M _Est determined from state variables in order to derive an actual compression efficiency.

For this purpose, in step S1 first a cylinder mean pressure p _{mi is} measured by means of a cylinder pressure sensor or estimated using a MWF method (MWF: Mechanical Work Feature) from a speed signal of the crankshaft. Such as from the DE 10 2008 054 690 A1 This is known to be the actual acceleration of the Driveline determined by the combustion and estimated from the introduced energy and the torque used for it. The speed signal contains information about a difference in converted physical energy or work during the burns, which behaves like the combustion chamber pressure pmi. For this purpose, the energy of the crankshaft is respectively calculated at a selected time or at a predetermined crankshaft angle before and after the combustion in the respective cylinder from the speed signal and determines the difference. This difference represents a measure of the physical energy or work converted by the respective combustion.

The cylinder mean pressure p _mi is determined as the mean value of the pressure curve in a cylinder during a power stroke. Furthermore, a focal point of combustion can be determined. The center of gravity of the combustion corresponds to that crankshaft angle at which half of the total fuel burning during a power stroke is burnt.

The combustion focus position can be derived from a cylinder pressure curve in a conventional manner. A cylinder pressure profile can be measured directly when providing a combustion chamber pressure sensor. However, if, as usual, no combustion chamber pressure sensor is provided, the center of gravity and the mean pressure of a combustion can be estimated based on the evaluation of a speed signal of the internal combustion engine.

wobei V_h dem Hubvolumen im Zylinder entspricht.The cylinder center pressure p _mi corresponds to a size to judge the efficiency and the charge cycle of reciprocating engines. The indicated cylinder mean pressure p _mi can be calculated from the specified torque or the work W _I delivered in the combustion chamber during a complete working cycle.

where V _h corresponds to the displacement in the cylinder.

In step S2, the actual actual torque M _Est is calculated from the cylinder mean pressure p _{mi in} accordance with the above formula.

In step S3, from a known model calculation based on manipulated variables for position encoders in the engine system, such as a throttle position, an intake manifold pressure and the like, a model _value of the actual engine torque M _{Mdl of} the internal combustion engine 2 and further modeling a compression _efficiency η _Mdl accordingly.

These sizes have an accuracy that results from the model accuracy. It was recognized that an error of a modeled actual engine torque M _{Mdl is also} reflected in the same way on an error of the modeled compression _efficiency η _Mdl . Thus, a moment balance can be created as follows: M _Est η _Est = M _Mdl · η _Mdl where η _Est corresponds to the actual compression efficiency.

Based on the above thermal efficiency formula, the actual compression efficiency η _Est can be derived

Thus, for the actual compression ratio ε _Est :

In step S4, the compression ratio ε _{Est is} calculated based on the actual compression efficiency η _Est .

Based on the thus-calculated compression ratio ε _Est , an error treatment can be performed in step S5. The calculated compression ratio ε _Est can in particular be used to check the position of the VCR actuator 6 and used to detect an unachieved actuator position. For this purpose, the calculated compression ratio ε _{Est is} compared with the compression ratio to be set for the determination of the VCR control variable, and when a tolerance threshold is exceeded, a corresponding error reaction is triggered by the difference between the calculated compression ratio ε _Est and the compression ratio to be set on the basis of the VCR control value , In particular, too great a deviation can be signaled in a suitable manner. In particular, based on the deviation between the calculated compression ratio ε _Est and the compression ratio to be set on which the VCR control variable is based, an error of the VCR actuator can be determined 6 getting closed.

In particular, this method can be used to check the plausibility of any VCR position sensor used. Alternatively, if there is no VCR position sensor, a Feedback on reaching the actual position of the VCR controller are derived.

In 3 is a schematic representation of an adaptation unit 15 for a VCR controller 6 of the internal combustion engine 2 shown. This can be done in a corresponding calculation block 14 calculated compression ratio ε _{Est can be used} for adapting a VCR actuator system. The adaptation unit 15 includes a regulatory block 17 , The regulatory block 17 a difference between the calculated compression ratio ε _{Est of} the internal combustion engine and a predetermined target compression ratio ε _{set desired} , which in a subtraction element 16 is determined. This difference is made with the help of a control element 17 , such as As a PI controller, in a VCR control variable for the VCR controller 6 implemented. This may cause an adjustment error of the VCR controller 6 be compensated with the help of a suitable regulation.

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

• WO 2014/019684 [0003]
• DE 102008050827 A1 [0004]
• US 2014/0014071 [0005]
• DE 102008054690 A1 [0037]

Claims (11)

Method for operating an internal combustion engine ( 2 ) with a VCR controller ( 6 ) for setting a compression ratio in a cylinder ( 3 ) of the internal combustion engine ( 2 ), in particular based on an indication of an actual compression ratio (ε _Est ), comprising the following steps: - determining a modeled actual engine torque (M _Mdl ), a modeled compression _efficiency (η _Mdl ) and an actual actual engine torque (M _Est ); Determining an actual compression efficiency (η _Est ) based on a moment balance; and - determining the actual compression ratio (ε _Est ) depending on the actual compression efficiency (η _Est ). The method of claim 1, wherein an error is signaled when the actual compression ratio (ε _Est ) of a predetermined target compression ratio (ε _target ), in particular by more than a predetermined tolerance value, deviates. Method according to claim 1, wherein a VCR manipulated variable for setting the VCR controller ( 6 ) is adapted based on the actual compression ratio (ε _Est ). The method of claim 3, wherein the VCR control variable depending on the actual compression ratio (ε _Est ) and the target compression ratio (ε _target ) is controlled. Method according to one of claims 1 to 4, wherein the actual actual engine torque (M _Est ) from an indication of the cylinder center pressure (p _mi ) is determined in particular depending on a stroke volume (V _h ) of a cylinder. Method according to claim 5, wherein the cylinder mean pressure (p _mi ) is determined by means of a curve of a measured cylinder pressure or by means of a profile of the rotational speed of a crankshaft of the internal combustion engine ( 2 ) is determined Device for operating an internal combustion engine ( 2 ) with a VCR controller ( 6 ) for setting a compression ratio in a cylinder ( 3 ) of the internal combustion engine ( 2 ), the apparatus being configured to: - determine a modeled actual engine torque (M _Mdl ), a modeled compression _efficiency (η _Mdl ) and an actual actual engine torque (M _Est ); To determine an actual compression efficiency (η _Est ) based on a moment balance; and to determine an actual compression ratio (ε _Est ) depending on the actual compression efficiency (η _Est ). Apparatus according to claim 7, wherein an adaptation unit is designed to generate a VCR control variable for controlling the VCR controller ( 6 ) by means of a control depending on a difference between the actual compression ratio (ε _Est ) and a predetermined target compression ratio (ε _target ) to determine. Engine system ( 1 ) with a drive motor ( 2 ) and a device according to claim 7 or 8. Computer program adapted to carry out all the steps of a method according to one of Claims 1 to 6. Machine-readable storage medium on which a computer program according to claim 10 is stored.

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