EP2598734A1

EP2598734A1 - Method for operating a reciprocating piston engine

Info

Publication number: EP2598734A1
Application number: EP11726073.7A
Authority: EP
Inventors: Marc Wodischek; Simone NOWAK; Bernd-Heinrich Schmitfranz; Tilmann RÖMHELD; Michael Wagenplast; Dieter Nowak
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2010-07-28
Filing date: 2011-06-11
Publication date: 2013-06-05
Also published as: US20130333670A1; CN103026030A; WO2012013262A1; DE102010032486A1; JP2013532791A

Abstract

The invention relates to a method for operating a reciprocating piston engine, in particular for a motor vehicle, in which a compression ratio of at least one cylinder of the reciprocating piston engine, in which a piston (30) is received so as to be guided in a translatorily movable manner, is adjusted by means of a servomechanism (38) corresponding to the cylinder, wherein a final control element (36), in particular a control piston (36), that is movably held at a guide (41) of the servomechanism (38) is moved between at least two positions, wherein the adjusted compression ratio is determined depending on at least one signal characterising at least one of the positions and detected by means of at least one detection device (50).

Description

Method for operating a reciprocating piston engine

The invention relates to a method for operating a reciprocating engine specified in the preamble of claim 1. Art.

DE 199 55 250 A1 discloses a method for monitoring the function of a

Device for variably adjusting the cylinder compression in a reciprocating internal combustion engine. In this case, before and after a control of the device for changing the cylinder compression, a Motorbethebsparameter on a

Change in the cylinder compression reacts, determined. Both values of the

Engine operating parameters are then compared with each other to determine whether a change in the engine operating parameter has occurred, wherein a change in the engine operating parameter is indicative of a correct operation of the cylinder compression variable adjustment device.

From WO 01/34948 A1 a method for controlling the cylinder compression during the starting phase of an internal combustion engine is known, which is equipped with a device for changing it compression end pressure. Before switching on a starter of the internal combustion engine, one or more criteria for a difficult starting the machine are checked. If at least one difficult starting criterion is met, the cylinder compression of at least one cylinder is reduced to a predetermined minimum value until the engine speed has ramped up to a defined threshold, then cylinder compression is increased.

From EP 1 431 59 A2 an air intake control device for an engine is known to be known which comprises a mechanism for variably adjusting an amount of intake air which controls an amount of fresh air flowing into the engine. Further, a mechanism for variably adjusting a

Compression ratio provided, which a compression ratio of the engine variable controls. Sensors detect operating conditions of the engine as well as the

A compression ratio, wherein a controller is configured to be electronically connected to the sensors, the variable intake air amount adjusting mechanism, and the compression ratio variable compression mechanism, to use the variable intake air amount adjusting mechanism Compression ratio and of the

Operating conditions of the engine to control.

DE 38 25 369 A1 discloses a device for controlling the

Compression ratio of an internal combustion engine, with a mechanism for changing the compression ratio of the internal combustion engine, at least between a first higher and a second lower stage, corresponding to

Engine operating conditions. Further, a compression ratio measuring means is provided for determining the current compression ratio. In addition, the apparatus includes sensor error detecting means for detecting a malfunction of the compression ratio measuring means, and a guard for changing and maintaining the compression ratio at the lower stage when the sensor error detecting means malfunctions the

Compression ratio measuring device detects.

From DE 10 2004 031 288 A1 an internal combustion engine with a

map-controlled, variable compression ratio as known, which is a load detection, a load request detection and an actuator for

Adjustment of the compression ratio includes. Further, a motor controller is provided, which is in communication with a time signal generator, wherein the

Motor control for determining the variable to be set

Compression ratio in a region of the internal combustion engine signal lines for detecting at least a part of the engine load. In addition, the internal combustion engine includes an integrated into the engine control

Comparator, which determines from the signals transmitted via the signal lines concerning at least the load in comparison with at least values from a predefinable characteristic map an optimized compression ratio.

DE 10 2006 033 062 A1 discloses a method for automatically determining a current compression ratio of a reciprocating piston engine during operation, wherein the reciprocating piston engine has a variable compression volume and a measurable crank angle, wherein by means of a relative to a sensor moving Part of a piston engine generates a signal and by means of the signal in relation to the crank angle standing trigger angle is determined, which is included in a determination of the current compression ratio.

US 6 857 401 B1 discloses a device for detecting a variable

Compression ratio for an internal combustion engine with a crankshaft and at least one piston, wherein the device is a connecting rod with a variable

Compression ratio comprises, via which the piston is connected to the crankshaft. The connecting rod has a plurality of discrete states for setting the compression ratio. There is provided a digital output sensor for generating a signal, the signal having a value corresponding to a particular state of the connecting rod. In this case, the sensor comprises a Hall sensor, which generates a signal that lasts longer, that corresponds to a high compression ratio. The Hall sensor generates a shorter duration signal, which corresponds to a low compression ratio.

The known reciprocating engines and methods have potential, a

Adjust set compression ratio of the reciprocating engine more precisely.

It is therefore an object of the present invention to provide a method for operating a reciprocating engine, which provides a more precise setting of the

Compaction ratio allows.

This object is achieved by a method for operating a reciprocating engine having the features of patent claim 1. Advantageous embodiments with expedient and non-trivial developments of the invention are specified in the remaining claims.

In such a method for operating a reciprocating engine, in particular for a motor vehicle, a compression ratio of at least one cylinder of the

Reciprocating piston engine, in which a piston guided translationally movable

is received, adjusted by means of a corresponding actuator to the cylinder, wherein a movably held on a guide of the adjusting device actuating part, in particular a control piston is moved between at least two position.

According to the invention it is provided that the set compression ratio in

Depending on at least one detected by at least one detection device and at least one of the positions characterizing signal is determined. The inventive method allows due to the detection of at least one position, in particular at least almost all position, the control part a very precise determination of the set compression ratio of the corresponding

Cylinder. To determine the compression ratio, other variables such as leverage, distance and / or angular relationships as well as other trigonometric relationships are optionally taken into account. Accordingly, in any way, the compression ratio can be adjusted precisely and as needed by precisely determining the compression ratio for controlled or controlled, staged or continuous adjustment of the compression ratio

Compression ratio is used.

The determination of the compression ratio according to the invention also makes it possible to compare the compression ratio set as the actual compression ratio with a desired setpoint compression ratio to be set. If the actual compression ratio deviates from the nominal compression ratio, which may occur, for example, as a result of wear during a very long service life of the reciprocating piston engine, then suitable countermeasures can be initiated in order to compensate for this deviation. In this case, for example, a readjustment

performed so that the set actual compression ratio at least in

Substantially matches the desired target compression ratio. This allows a very efficient, low-emission and low-energy consumption, especially low fuel consumption, operation of the reciprocating engine and that even with a very long life and a very long service life derselbigen.

It is also possible that by means of the detection means a distance traveled by the control part between the positions, i. a stroke, the control part is detected, allowing the precise determination and thus the precise adjustment of the

Densification ratio benefits.

As already indicated, the control element is designed, for example, as a control piston, which comprises a control rod and a piston connected to the control rod, which piston is acted upon in a cylinder which can be acted upon by a working medium

Actuator is slidably guided out. The cylinder forms the

Guiding the adjusting device. The control piston is formed for example as a hydraulic piston and actuated as a result of an actuation of the cylinder with a hydraulic fluid, wherein the admission, ie a supply and a discharge of Hydraulic fluid is controlled in the cylinder or out of the cylinder, for example via an electromagnet.

In contrast to such an active setting and a passive adjustment is possible in which the piston is moved due to gas and assenkräften the reciprocating engine, which act for example via a piston in the cylinder on the control piston and thus on the piston of the actuator. The plunger of the actuator is released by the working fluid and valve means, for example check valves, which are connected via other control valves, for example a control spool with control edges, which release or block lines for the working fluid, released in a desired direction of movement and opposed in the desired direction of movement

Movement direction blocked or completely held. It is a kind of hydraulic freewheel. This embodiment has the advantage that a desired compression ratio can be set without and with only a very small additional energy input.

Is also possible that the actuator as an electromagnet or as part of a

Electromagnet is formed and thus on the operating principle of such

Electromagnet for adjusting the compression ratio is actuated.

Further, it is possible that the control piston is designed as a pneumatic piston, which can be actuated by applying pressure to the cylinder with compressed air. The

Actuation of the cylinder, so the supply or discharge of compressed air into the cylinder or out of the cylinder can be controlled or regulated via an electromagnet.

In any regard, the advantage of using such an electromagnet has the advantage that this makes the adjusting particularly quickly adjustable and thus the

Compression ratio is particularly fast and needs changing

Operating points or at current present operating point of the reciprocating engine is adaptable.

The detection of the position of the actuating part makes it possible to check whether the desired compression ratio is actually set. If this is not the case, readjustment or readjustment can be carried out if necessary and until the desired compression ratio has actually been set and the control element has been adjusted takes the necessary position. As a result, the assumption of the required position by the adjusting member negatively influencing factors, such as deposition due to wear or the like, can be compensated. For this purpose, for example, the signal characterizing the position is compared with one or more characteristic values stored, for example, in a control or regulating device of the reciprocating engine, and checked for a deviation or an exceeding or undershooting of a threshold value by such a deviation.

In an advantageous embodiment of the invention, the detection device comprises at least one transmitter part, in particular a magnet and in particular one

Permanent magnets, as well as a corresponding detection part, in particular a detection plate, wherein the transmitter part, for example, on the control part and the detection part on a housing of the reciprocating engine, to which the control part and the guide are pivotally mounted together about a pivot axis, are arranged. It is also possible that the detection part on the control part and the transmitter part are arranged on the housing. In other words, in an operation of the reciprocating engine, the detection part and the transmitter part move relative to each other, since the adjusting device and thus the control part in the operation of the reciprocating engine

Performs movements and moves, for example, with a mounted on a crank pin of a crankshaft of the reciprocating engine transverse lever and relative to the housing, in particular a crankcase of the reciprocating engine and / or a surrounding the adjusting device housing moves. This allows a particularly precise detection of the position of the control part and as a result a particularly precise and needs-based adjustment of the compression ratio, which leads to an efficient, low-emission and low-energy consumption operation of the reciprocating engine.

If the detection device comprises a Hall sensor, to which the detection part and the transmitter part are assigned, this has the advantage that the position can be detected particularly precisely and particularly robustly and consequently the compression ratio can be determined and adjusted particularly precisely.

In a particularly preferred embodiment of the invention, the detection part and / or the transmitter part are curved, in particular convex - formed with respect to the pivot axis. This avoids or at least reduces a negative impact on the determination of the compression ratio due to any angular error due to the relative movement, in particular the relative pivoting of the detection part and the transmitter part to each other. This comes the precise detection of the position and thus the Particularly precise determination of the compression ratio particularly beneficial. A particularly precise determination of the compression ratio is possible if the curvature of the transmitter part and / or the detection part of the pivoting movement corresponds, for example, the center of the curvature lies on the pivot axis. As a result, there is no or only to a very limited extent angular errors in the relative movement of the detection part and the encoder part to each other, resulting in a very accurate detection of the position of the actuator results.

Particularly advantageously, a magnetic field of the encoder part is curved, in particular with respect to the pivot axis convex, formed, wherein preferably the center of the curvature lies on the pivot axis and thus corresponds to the curvature of the relative movement, in particular the relative pivoting of the transmitter part and the detection part to each other. As a result, the position of the control can be determined very precisely and consequently the compression ratio very accurately, so that by using the determined compression ratio for setting a desired compression ratio of this very accurately and as needed by means of

Setting device can be adjusted.

In a further embodiment, the detection device is an optical

Detection device which comprises a reflection part, in particular a reflection plate. The emitting part of the optical detecting means emits rays which are reflected by the reflecting part and detected by the detecting part.

For example, as a function of the time period between the emission of the rays and the detection of the rays reflected by the reflection part through the

Detecting part can detect the position of the control part particularly quickly and precisely and as a result, the compression ratio can be determined very accurately and just as quickly. This is particularly advantageous in that even with rapidly changing operating points of the reciprocating engine and accordingly quickly adjusted and rapidly changing compression ratios dieselbigen to determine very quickly and adjust particularly quickly. Analogous to the detection part or the transmitter part, the reflection part is arranged, for example, on the setting part or on the housing, on which the adjusting part or the adjusting device moves at least during operation of the reciprocating piston engine.

If the signal is synchronized with a rotational position of the crankshaft of the reciprocating engine, which is also referred to as a crankshaft angle degree ([° CA]), and thus the position or the signal characterizing the position in relation to the degree crank angle set, so the compression ratio is thereby to be determined particularly accurately because the detected position of the control part is clearly assigned a compression ratio and any ambiguities are avoided. Even in the case of the curved transmitter part and / or the curved detection part, a signal characterizing the position of the actuating part can occur which, albeit only slightly, is emitted by the control unit

actual position of the control part deviates. The detected rotational position

(Degree crankshaft angle) of the crankshaft uniquely characterizes a position on the detection part or the control part, which makes it possible to increase said deviation

compensate.

This deviation of the detected from the actual position can be determined for example on the basis of experiments and stored for example in a map of a control or regulating device of the reciprocating engine and is thus known, so that this error as a function of the known, because detected compensated, rotational position and the detected position of the control part so at least in

Be adapted or adapted to the actual position.

From the map, for example, a correction value is read in accordance with the detected rotational position, by means of which the detected position is corrected. The detection of the position of the actuating part makes it possible to check whether the position of the actuating part is at least substantially within a certain range and thus the actuating device or the actuating part has a desired functionality. If the position is outside this range, this indicates a malfunction of the control part, so that appropriate countermeasures must be taken to avoid damaging operation of the reciprocating engine or the actuator or operation of the reciprocating engine with an undesirably high energy consumption and undesirably high emissions. Thus, the detection of the position of the actuating part allows, in particular by the described compensation in dependence on the rotational position of the crankshaft on the one hand a particularly precise detection of the position and thus a particularly precise adjustment of the compression ratio and on the other hand, the verification of the adjusting device or the actuating part to a desired functionality.

As a result, a hysteresis compensation is realized, by which a deviation of the position of the actuating part is compensated in its from the actual position. This is particularly advantageous in a range of so-called end stops of the actuating part. These areas are respective end regions of a Movement range, in particular a pivoting range, the actuating part, in which moves the actuator during operation of the reciprocating engine or to the

Pivot axis pivots back and forth. In these end regions may possibly be particularly large deviations. In addition, this is

Hysteresis compensation advantageous if the setting part for setting the maximum or minimum adjustable compression ratio has its maximum or minimum stroke and maximum retracted or extended. Even with such a

Maximum or minimum stroke may possibly be given relatively large deviations. These can be compensated by the hysteresis compensation.

Preferably, an analog transmission of the position characterizing signal is performed in particular to a control or regulating device of the reciprocating engine, which has the advantage that thereby a continuous signal transmission with very high sampling rates is possible, the precise detection of the position and thus the precise determination of the Densification ratio benefits.

As already described, a particularly precise determination of the

Compaction ratio and thus a particularly precise adjustment desselbigen allows when a deviation of the determined based on the signal position of the adjusting part of a set in a map in a table or the like specified position corrected and the determined based on the signal position at least substantially to the actual Position is adjusted. This correction and adaptation can be carried out very precisely in particular if the deviation is dependent on a generation of the signal by the detection device and / or on a duration of a transmission of the signal to the control or

Control device of the reciprocating engine and / or of a duration of a

Signal conditioning of the signal and / or from a computing power of the control or regulating device of the reciprocating engine is corrected and adjusted.

Possible, the signal or its generation and detection negatively affecting disturbances can be compensated by a model-based filtering. Such model-based filtering ensures that no surreal dynamics of the

Reciprocating piston or the adjusting device as a current, the reciprocating engine or the adjusting device characterizing variables are taken into account and so

if applicable, adversely affect the determination of the compression ratio. Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawing. The features mentioned above in the description and

Feature combinations as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures are not only in the respectively indicated combination but also in others

Combinations or in isolation usable without departing from the scope of the invention.

The drawing shows in:

Fig. 1 a detail of a schematic side view of a crank mechanism for a reciprocating engine with a plurality of cylinders and the cylinders associated pistons, wherein by means of the crank mechanism respective compression ratios of the cylinder cylinder individually independently adjustable;

Fig. 2 shows a detail of a schematic side view of the crank mechanism according to

Fig. 1 with a schematic diagram for detecting a position of a

Control piston of an adjusting device for adjusting the

Compression ratio, wherein based on the detected position of the control piston, the set compression ratio of the corresponding cylinder is determined;

3 shows a schematic side view of an embodiment of the crank mechanism according to the preceding figures with a bipolar encoder plate of a detection device of the adjusting device, which is designed to be curved in the same way as its magnetic field;

4 shows a schematic view of the curved encoder plate and its curved magnetic field according to FIG. 3;

Fig. 5 is a schematic view of a course of the curved magnetic field of the encoder plate of FIG. 3 in a movement of the adjusting device and a schematic view of a contrast straight

Magnetic field of such movement of the actuator; and Fig. 6 is a schematic diagram for compensating a deviation of one of the

Encoder plate according to FIG. 3 detected position of the adjusting device of an actual position of the adjusting device.

Fig. 1 shows a crank mechanism 10 for a reciprocating engine of a motor vehicle, wherein the reciprocating piston engine comprises a plurality of cylinders. For the sake of clarity, the crank mechanism 10 will be described with reference to FIG. 1 with respect to one of these cylinders corresponding to the crank mechanism 10 of the reciprocating piston engine. It is understood that the description of the crank mechanism 10 and the cylinder is analogous to the other cylinders of the reciprocating piston engine, in particular all others.

The crank mechanism 10 comprises a crankshaft 12, which has main bearing points, via which the crankshaft 12 is mounted in a crankcase of the reciprocating engine. Furthermore, the crankshaft 12 crank webs, of which such a crank arm 14 is shown in FIG. 1. In addition, the crankshaft 12 crank pin, of which a crank pin 16 is shown in FIG. The crank pin 6 corresponds to a cylinder of the reciprocating engine. In the same way, the other crank pins correspond to a cylinder of the same

Reciprocating engine.

Furthermore, the crank operation 10 includes a transverse lever 18, which is a first

Lever element 20 and a second lever element 22 includes, which are connected to each other, for example, screwed together, are. The transverse lever 18 is rotatably mounted on the crank pin 16 relative to this about an axis of rotation 25 and performs strokes in a rotation of the crankshaft 12, for example, during operation of the reciprocating engine, with out.

The transverse lever 18 has a first bearing 24, on which a connecting rod 26 of the crank mechanism 10 is articulated. In this case, the connecting rod 26 can rotate about a rotation axis 28. As can be seen from FIG. 1, the axis of rotation 28 is spaced from the axis of rotation 25 in the radial direction of the crank pin 16 by a first lever arm 11.

The crank mechanism 10 also includes a piston 30, which corresponds to the cylinder, to which the crank pin 16 corresponds, and in which the piston 30 is received translationally movable. The piston 30 is pivotally connected to the connecting rod 26 via a further bearing 32. Attached is the piston 30 to the connecting rod 26th via a piston pin in the piston 30 by a corresponding

Circlip is secured in the axial direction of the piston pin. If the piston 30 is moved translationally in the cylinder as a result of combustion processes, this translational movement is converted via the connecting rod 26, the transverse lever 18 and the crankpin 16 into a rotational movement of the crankshaft 12.

The transverse lever 18 has a further bearing 34, on which a control piston 36 of an adjusting device 38 of the reciprocating engine articulated and with the

Cross lever 18 is connected. In this case, the control piston 36 can rotate about an axis of rotation 40 of the bearing 34. The axis of rotation 40 is spaced by a further lever h ₂ in the radial direction of the crank pin 16 of the rotation axis 25. It can be seen that the levers and h ₂ differ in terms of amount. The lever h ₂ is larger than the lever hi. It is also possible that the levers and h ₂ are equal in magnitude, or that the lever is larger than the lever h ₂ . In addition to

Control piston 36, the adjusting device 38 comprises a housing 41 through which a cylinder is formed. In the cylinder, the control piston 36 is held translationally guided guided. By supplying or removing a working medium into the cylinder, for example compressed air, hydraulic fluid or the like, the control piston 36 can be moved translationally in accordance with a directional arrow 43 and extended with respect to the housing 41 according to a directional arrow 44 or retracted according to a directional arrow 46. In contrast to such an active attitude is also a passive one

Adjustment possible, in which the control piston 36 is moved as a result of gas and inertial forces of the reciprocating engine, which act on the piston 30 on the control piston 36. The control piston 36 is released by the working fluid and valve means, for example check valves which are connected via other control valves, for example, a control slide with control edges which lines for the working fluid release or obstruct, in a desired direction of movement and opposite in the desired direction of movement

Movement direction blocked or completely held. It is a kind of hydraulic freewheel. This embodiment has the advantage that a desired compression ratio can be set without and with only a very small additional energy input. It is also possible to actuate the control piston 36 by means of an electromagnet.

If the crankshaft 12 rotates, the crank pin 16 moves up and down, which also leads to a movement of the transverse lever 18. The adjusting device 38 also moves by the housing 41 pivotable about a pivot axis 42 at a Adjusting device 38 surrounding housing, for example, on a crankcase of the reciprocating engine, is mounted.

If the control piston 36 is moved translationally according to the directional arrow 43, this leads to a rotation of the transverse lever 18 relative to the crank pin 16 according to a directional arrow 48, whereby the compression ratio of the corresponding cylinder can be adjusted. In this case, the adjustment of the control piston 36 acts on the ratio of the levers hi and h _{2 to} the same extent, reinforced or reduced. In other words, the adjustment of the control piston 36 leads to an adjustment or adjustment of the top dead center of the piston 30 in the cylinder and thus to an adjustment or adjustment of the compression volume v _{c of} the corresponding cylinder. The adjustment of the control piston 36 also affects the stroke and thus the stroke volume v _{H of} the piston 30. The stroke volume v _H reduces as the flow increases

Compression ratio, which is desirable in terms of the downsizing concept. This results in a corresponding compression ratio, which is also referred to as ε:

As already indicated, advantageously, each of the cylinders of the reciprocating engine associated with such a control device 38, by means of which the compression ratio of the corresponding cylinder can be adjusted independently of the other cylinders. This cylinder-specific adjustment of the corresponding compression ratios allows a very precise and extremely needs-based adjustment of

Reciprocating engine to present operating points, so that the reciprocating engine very efficient, low emissions and energy consumption, in particular

low fuel consumption, can be operated.

For precise and needs-based adjustment of the compression ratio, it is desirable to determine the set compression ratio and

if necessary check. This is possible, for example, in which the position of the control piston 36 relative to a reference point and / or the distance covered during the movement of the control piston 36 way, so the stroke of the control piston 36 to detect, and starting therefrom, inter alia, in dependence on the levers n and h ₂ , the connecting rod 26, etc. on the set compression ratio infer or determine this. A position or the stroke of the control piston 36th

characterizing signal can then be used to control or regulate the

Compression ratio can be used to adjust this variable, continuously or stepwise. This is illustrated by the schematic diagram in FIG. 2. A schematically illustrated in FIG. 2 sensor 50 detects the position of the control piston 36 and a

Control rod this relative to a reference point and / or the stroke of the control piston 36 and a position and / or the stroke characterizing signal. This signal is transmitted according to a directional arrow 52 to a position control 54 of a control device 56, wherein the control device 56 is formed, for example, as a control unit of the reciprocating engine. The control device 56 further comprises a combustion control 58, by means of which the combustion processes in the cylinders of the reciprocating engine are controlled or regulated. Considering that

Combustion control 58, inter alia, a feedback 60 of the set actual compression ratio, which is determined by the position control 54 based on the signal detected by the sensor 50 and thus based on the position of the control piston 36. For adjusting the compression ratio and for adjusting desselbigen transmitted to an operating point of the reciprocating engine transmits the

Combustion control 58 a preset 62 of a target compression ratio to the position control 54, which converts the target compression ratio in a position to be adjusted of the control piston 36. For this purpose, the position control 54 also takes into account any other system variables 64 of the crank mechanism 10 and the

Reciprocating engine.

The determined position for setting the desired compression ratio or a position of the control piston 36 characterizing signal is transmitted to a control 65 for the control device 38, which transmits corresponding control signals to an actuator 66, by means of which the control piston 36 moves and thus the

Compression ratio is set.

FIG. 3 shows a possibility of detecting the position of the control piston 36 in order to precisely determine the set compression ratio as a function of this position and to set it precisely in the sequence. For this purpose, the sensor 50 comprises a bipolar encoder plate 70, which is shown schematically in FIG. 4 and has a magnetic field 72. The encoder plate 70 is formed curved like its magnetic field 72, wherein the center of the curvature lies on the pivot axis 42. This causes the curvature of the encoder plate 70 and the magnetic field 72 to correspond to the pivotal movement of the control piston 36, which the control piston 36 during operation of the

Reciprocating piston when pivoting about the pivot axis 42 according to a

Directional arrow 68 executes. The term "north" in FIG. 4 designates the north pole of the magnetic field 72, while the term "south" in FIG. 4 designates the south pole of the magnetic field 72. A curved line 74 indicates a boundary between the north pole and the south pole and illustrates that the magnetic field 72 is curved. Another line 76 in FIG. 4 indicates an imaginary boundary of a non-curved but straight magnetic field of the encoder plate 70. Likewise, a detection part 78 of the sensor 50 is shown in FIG. 4, by means of which the magnetic field 72 for detecting the position of the control piston 36 is to be detected.

The sensor 50 detects the orientation of the magnetic field 72 over the

Detecting part 78, the current position or the current stroke of the control piston 36 for adjusting the compression ratio, ie how far the control piston 36 is extended or retracted from the housing 41. This position characterizes this

Compression ratio. If a certain compression ratio is maintained, the translational position according to the directional arrow 43 of the control piston 36 also remains constant. Nevertheless, the control piston 36 rotates during operation of the reciprocating piston by the control piston 36 pivots about the pivot axis 42 according to the directional arrow 68 and thereby performs a swinging motion.

For precise detection of the translational position of the control piston 36 also during this oscillating movement, the encoder plate 70 and its magnetic field 72 is curved and has a correspondingly large extent in the direction of movement of the control piston 36 for adjusting the compression ratio according to the

Directional arrow 43. This ensures that the detection member 78 is always at least partially, in particular predominantly and in particular completely, in registration with the encoder plate 70. The arcuate design of the encoder plate 70 and the magnetic field 72 avoids or reduces at least one angle error, which is given unequally greater or even at a straight magnetic field.

This is shown in FIG. 5. FIG. 5 shows a diagram 78, on the abscissa 80 of which time and on whose ordinate 82 a variable characterizing the magnetic field 72 is plotted. A trace 84 in the diagram 78 gives a behavior of the

Magnetic field 72 characterizing size of one in the diagram 78th

applied period in which the reciprocating engine is in operation and accordingly the control piston 36 oscillates about the pivot axis 42. Since the magnetic field 72 is curved, the magnitude characterizing the magnetic field 72 remains constant. Thus, on the basis of the magnetic field 72 characterizing size clearly determine the correspondingly set compression ratio. A

Variation of the magnetic field 72 characterizing size, as in the

Diagram 78 is indicated in a region 86, results only in that the control piston 36 moves in translation according to the direction arrow 43 and thus the compression ratio is changed. The pivoting or oscillating movement of the control piston 36 about the pivot axis 42 influences the magnetic field 72

characterizing size not.

In contrast, in the diagram 78, a further course 88 is shown, which reproduces the behavior of a magnetic field characterizing variables, which in contrast to the magnetic field 72 and line 76 correspondingly straight formed and formed for example by an equally straight encoder plate.

As can be seen from the course 88, there is a swinging movement, which corresponds to the oscillatory movement of the control piston 36 about the pivot axis 42 and represents a difficult to handle and little meaningful signal for detecting the position of the control piston 36 for adjusting the compression ratio. The comparison of the curves 84 and 88 shows that the position of the control piston 36 for adjusting the compressor ratio, ie in the translational direction according to the directional arrow 43, by the curved magnetic field 72 substantially more precise and

more meaningful to grasp.

FIG. 6 shows a further possibility of detecting the position of the control piston 36 in a particularly precise and accurate manner, and thereby determining the set compression ratio particularly precisely. 6 shows a diagram 90 in which a curve 92 of a signal is entered, the position of the control piston 36 detected by the encoder plate 70 and the magnetic field 72 at a set compression ratio and during the execution of the swinging movement about the pivot axis 42 characterized according to the directional arrow 68.

The characterizing the position signal is with one by means of another

Detected detecting rotational position, which is referred to as a degree crank angle, the crankshaft 12 of the reciprocating engine synchronized to compensate for a deviation of the detected position of the control piston 36 from the actual present position. In FIG. 6, a detection time 94 is entered. At the detection time 94 there is a corresponding position of the control piston 36, which is characterized by a value 96 characterizing the magnetic field 72. As can be seen from FIG. 6, however, even with the use of the curved encoder plate 70 and the curved magnetic field 72, in particular in end regions 98 of a swiveling range of the control piston 36 in which the control piston 36 is in operation

Reciprocating piston machine, a deviation of the detected position from the actual position before. This is the case, in particular, when the control piston 36 is extended to the maximum, as shown by a profile 100 or when the control piston 36 has retracted to the maximum, which is represented by a profile 102. In other words, the curve 100 provides a track of the oscillating motion of the

Control piston 36 at its maximum stroke, that is, when the control piston is maximally extended. The course 102, in other words, a career of

Oscillation movement of the control piston at a minimum stroke, so if the

Control piston 36 is retracted maximally. The curve 92 represents a nominal curvature of the magnetic field 72. The described deviation is characterized in the diagram 90 by a measurement error 104.

A compensation of this deviation or this measurement error 104 can be carried out on the basis of a characteristic field stored in the control device 56. Since the rotational position of the crankshaft 12 uniquely represents a position on the encoder plate 70, the error in the current detection time 94 can be compensated, since the measurement errors 104 were determined, for example, in tests and stored in the map. The maximum measurement error 104 is dependent on the deviation between the detected position of the control piston 36 and the associated degree crank angle. The measurement error 104 is composed of a duration for signal generation in the sensor 50, a duration for signal transmission, a duration for signal processing in the control device 56, and a duration of a computing time that the

Control means 56 for an allocation of the degree crank angle to the value 96 required. Daimler AG

LIST OF REFERENCE NUMBERS

10 crank drive

12 crankshaft

14 crank arm

16 crank pins

18 cross levers

20 lever element

22 lever element

24 storage location

25 axis of rotation

26 connecting rods

28 axis of rotation

30 pistons

32 storage location

34 storage location

36 control piston

38 adjusting device

40 axis of rotation

41 housing

42 pivot axis

43 directional arrow

44 directional arrow

46 directional arrow

48 directional arrow

50 sensor

52 directional arrow

54 position control

56 control device

58 combustion control

60 feedback 62 default

64 system sizes

65 control

66 Actuator

68 directional arrow

70 encoder plate

72 magnetic field

74 line

76 line

78 diagram

80 abscissa

82 ordinates

84 History

86 area

88 History

90 diagram

92 History

94 detection time

96 value

98 area

100 course

102 History

104 measurement error hi lever

h ₂ lever

Claims

claims

Method for operating a reciprocating piston engine, in particular for a motor vehicle, in which a compression ratio of at least one cylinder of the reciprocating piston engine, in which a piston (30) is received translationally guided, by means of a corresponding to the cylinder

Adjusting device (38) is set, wherein a on a guide (41) of the

Actuating device (38) movably held actuating part (36), in particular a

Control piston (36) is moved between at least two positions,

characterized in that

the set compression ratio is determined as a function of at least one signal detected by at least one detection device (50) and characterizing at least one of the positions.

Method according to claim 1,

characterized in that

the detection device (50) comprises at least one transmitter part (70), in particular a magnet (70), and a corresponding detection part (78), in particular a detection plate (78), wherein the transmitter part (70) on the setting part 36) and the Detecting part (78) on a housing of the reciprocating piston engine, to which the actuating part (36) and the guide (41) together relative to a

Swivel axis (42) pivotally, are, are arranged.

Method according to one of claims 1 or 2,

characterized in that

the detection device (38) at least one transmitter part (70), in particular a magnet (70), and a corresponding thereto detection part (78), in particular a detection plate (78), wherein the transmitter part (70) on a housing of the reciprocating engine, to which the actuating part (36) and the guide (41) are pivotable together about a pivot axis (42), and

Detecting part (78) on the adjusting part (36) are arranged.

Method according to one of claims 2 or 3,

characterized in that

the detection part (78) and / or the transmitter part (70) curved, in particular with respect to the pivot axis (42) convex, are formed.

Method according to one of claims 2 to 4,

characterized in that

a magnetic field (72) of the transmitter part (70) curved, in particular with respect to the pivot axis (42) convex, is formed.

Method according to one of the preceding claims,

characterized in that

the detection device (50) a Hall sensor or an optical

Detection device is.

Method according to one of the preceding claims,

characterized in that

the signal is synchronized with a rotational position of a crankshaft (12) of the reciprocating engine.

Method according to one of the preceding claims,

characterized in that

an analogue or a digital transmission of the signal to a

Control device (56) of the reciprocating engine is performed.

Method according to one of the preceding claims,

characterized in that

a deviation of the position of the actuating part (36) determined from the signal from an actual position given in a characteristic field, a table or the like corrected and the position determined by the signal at least in

Essentially adapted to the actual position.

10. The method according to claim 9,

characterized in that

the deviation as a function of a generation of the signal by the detection device (50) and / or a duration of a transmission of the signal to a control device (56) of the reciprocating engine and / or a duration of signal conditioning of the signal and / or of one

Calculation performance of a control device (56) of the reciprocating engine is corrected.