Variable compression ratio (VCR) engine

Abstract

To provide a variable compression ratio (VCR) engine with more continuous performance and with less need for maintenance than in the prior art.SOLUTION: The invention relates to a variable compression ratio (VCR) engine and a method for driving the variable compression ratio (VCR) engine. The variable compression ratio (VCR) engine 1 comprises at least one cylinder 2 with a piston 3 movably arranged therein and adapted to perform a predefined piston stroke, and a setting unit 4 for setting a preset compression ratio by setting a preset clearance position 11. The VCR engine 1 further comprises a control unit 5 for setting at least one temporal clearance 15 position different from the preset clearance position 11 and for inducing at least one piston movement with the temporal clearance position 15.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a variable compression ratio (VCR) engine and a method for operating a variable compression ratio (VCR) engine.

Background Art

[0002] In a reciprocating piston combustion engine, the compression ratio is an important parameter related to combustion, thermal efficiency, and also related to the emission of exhaust gases.

[0003] The compression ratio of a combustion engine represents the ratio of the maximum volume to the minimum volume of the combustion chamber volume of the combustion engine. In a piston engine, the compression ratio is the ratio of the volume of the cylinder and the combustion chamber when the piston is at the bottom of its stroke to the volume of the combustion chamber when the piston is at the top of its stroke. Therefore, the compression ratio can be calculated by the ratio of the sum of the displacement volume and the clearance volume to the clearance volume. The displacement volume is the volume inside the cylinder displaced by the piston from the start to the end of the compression stroke. The clearance volume is the volume of the space remaining in the cylinder at the end of the compression stroke.

[0004] The compression ratio is usually selected to provide the highest engine performance. Often, high-load engine performance is the most relevant item in that selection. To optimize performance over the entire operating range, it is desirable for the compression ratio to be variable.

[0005] In smaller reciprocating piston combustion engines, various solutions for changing the compression ratio are known, such as an eccentric sleeve around the piston pin or the main bearing, or an eccentric shaft and mechanism for adjusting the distance between the cylinder head and the crankshaft center line.

[0006] The compression ratio can be varied, for example, by allowing the gas to flow into an additional volume outside the cylinder as disclosed in European Patent No. 2677141 (A1), or by means of a movable exhaust valve seat as disclosed in Japanese Patent Application Laid-Open No. Sho 61-197731 (A).

[0007] Typically, a large reciprocating piston combustion engine has one or more cylinders each provided with a cylinder liner, one or more pistons movably disposed inside each cylinder liner, and a crankshaft rotatably disposed in a crankshaft housing. Each piston is connected to a respective crosshead via a piston rod, and each crosshead is connected to the crankshaft via a connecting rod to drive the crankshaft. Typically, the piston rod is linearly guided parallel to its longitudinal axis, and each crosshead converts the linear movement of the piston rod into a non-linear movement of the connecting rod.

[0008] European Patent No. 2687707 (A2) discloses a large reciprocating piston combustion engine in which the crosshead and / or the piston can be provided with a control device for controlling the compression ratio of the reciprocating piston combustion engine. For example, the piston rod can be extended by a hydraulic cylinder placed within the crosshead pin. Thereby, the maximum and minimum achievable positions of the piston are changed.

[0009] In a combustion engine, during long-term operation, carbon may accumulate on top of the piston top dead center, and wear steps may occur.

[0010] In the case of a fixed compression ratio, this is not a problem because the piston will never reach this range.

[0011] However, when changing the compression ratio by specifying the maximum and minimum positions of the piston within the cylinder, it can happen that the maximum piston positions of the piston, especially the uppermost piston ring, vary.

[0012] If the engine is operated for a long time at a "low" compression ratio with a relatively large clearance volume and then the compression ratio is suddenly increased, the piston rings will pass through the range of wear steps and carbonized deposits.

[0013] As a result, the reliability of the piston's operating performance is not guaranteed, and there is a possibility of damage to the piston, piston rings, and cylinder liners. In a variable compression ratio (VCR) engine, it is essential to manage carbon deposition and avoid wear steps to ensure the reliability of engine operation.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0015] It is an object of the present invention to provide a variable compression ratio (VCR) engine that avoids the drawbacks of the prior art and, in particular, has more sustainable performance and a lower need for maintenance than prior art engines, and a method for operating a variable compression ratio (VCR) engine.

Means for Solving the Problems

[0016] This object is achieved by a variable compression ratio (VCR) engine according to the independent claims and a method for operating a variable compression ratio (VCR) engine.

[0017] This object is achieved by a variable compression ratio (VCR) engine having at least one cylinder with a piston movably disposed within the cylinder and adapted to perform a predetermined piston stroke within the cylinder. The variable compression ratio (VCR) engine has a setting unit for setting a predetermined compression ratio by setting a preset clearance position.

[0018] The piston moves between bottom dead center and top dead center. The distance between these lowest and uppermost positions corresponds to the piston travel length that can be determined by the length of the crankshaft and the length of the connecting rod.

[0019] At top dead center, the piston is at the clearance position.

[0020] The preset clearance position is the uppermost position of the preset piston, in particular the uppermost position of the top ring, and corresponds to the respective clearance volume.

[0021] The top ring is a sealing ring disposed in the top groove of the piston.

[0022] During operation, since the cylinder diameter, piston, piston rod, connecting rod and crankshaft lengths are fixed, for a given piston / cylinder arrangement, the travel length, and thus the displacement volume, can rarely be changed. Therefore, setting the clearance volume defines the compression ratio.

[0023] Normally, within the cylinder there is the highest uppermost position achievable by the piston, and that position corresponds to the smallest achievable clearance volume and the largest achievable compression ratio.

[0024] To select a smaller compression ratio, the operating range of the piston within the cylinder can be moved to a lower clearance position, a larger clearance volume, and thus a smaller compression ratio can be achieved.

[0025] According to the present invention, the VCR engine further has a control unit for setting at least one temporary clearance position different from the preset clearance position and causing at least one piston movement at the temporary clearance position.

[0026] The temporary clearance position is preferably above the preset clearance position, that is, closer to the highest uppermost position that can be realized as the preset clearance.

[0027] The control unit is then preferably adapted to reset the preset clearance position and cause a piston movement at the preset clearance position.

[0028] The piston movement at the temporary clearance position is a movement between the lowermost position and the uppermost position, where the uppermost position corresponds to the temporary clearance position.

[0029] Preferably, a temporary clearance position corresponding to the absolute highest position of the piston, thus the minimum clearance volume, and the maximum achievable compression ratio is selected.

[0030] When a temporary clearance position corresponding to a smaller clearance volume is sometimes executed compared to the preset clearance position, carbon deposition can be reduced. While moving along the inner wall, the piston removes the dirt on the inner wall of the cylinder. Deposits of carbon substances that may accumulate on the inner wall of the cylinder in the region above the clearance position of the piston can be removed when the piston, especially the top ring, passes through this range.

[0031] The control unit is preferably adapted to cause at least one piston movement at the temporary clearance position according to at least one predetermined scheme.

[0032] The scheme preferably defines the temporary clearance position, the time interval or the number of strokes for holding the temporary clearance position, and / or the continuous values of the setting period.

[0033] The scheme may repeatedly cause the setting of the piston movement at a temporary clearance position corresponding to a smaller clearance volume compared to the preset clearance position after a predetermined time interval or after a predetermined number of piston stroke operations.

[0034] The scheme may provide a curve chart defining the clearance position with respect to time or the number of position strokes. According to this curve chart with respect to time or the number of piston strokes, the temporary clearance position is changed. The scheme may define a stepwise change in the temporary clearance position.

[0035] If the clearance position is changed by an overly fast or overly large distance change, there is a risk that the piston passes through a range having a wear step, and this risk should be prevented. By appropriately changing the clearance position, the piston gradually approaches a range where deposits may exist. The piston can gradually remove deposits over the entire curve chart of the change.

[0036] Furthermore, it may take some time to remove deposits. Therefore, the scheme can define the time for which a temporary clearance value is maintained or the number of piston strokes.

[0037] In an advantageous embodiment of the VCR engine, the control unit is adapted to cause piston movement at a temporary clearance position in response to a request.

[0038] Alternatively, or in addition, the control unit is adapted to cause at least one piston movement at a temporary clearance position per 100 to 5000000 piston strokes.

[0039] Alternatively, or in addition, the control unit is adapted to cause at least one piston movement at a temporary clearance position per 1 hour to 2 months of operating time.

[0040] The VCR engine may have at least two cylinders, and the control unit can be adapted to cause piston movement at a temporary clearance position for the selected cylinder. The other cylinders can perform a preset piston stroke at a preset clearance position to provide a preset combustion, a preset thermal efficiency, and a preset exhaust gas emission. The control unit can be adapted to select each cylinder according to at least one predetermined scheme.

[0041] The VCR engine may have at least two cylinders, and the control unit can be adapted to cause piston movement at a temporary clearance position for all cylinder pistons simultaneously or one cylinder at a time.

[0042] The VCR engine may have several assembled cylinders, the number of which is at least three, and the control unit can be adapted to simultaneously cause piston movement at a temporary clearance position for some of the assembled cylinders. The number can be between two and the number of assembled cylinders minus one.

[0043] Therefore, there is always a cylinder that performs a preset piston stroke at a preset clearance position.

[0044] In a preferred embodiment of the VCR engine, the control unit is adapted to cause piston movement at the maximum compression ratio at each start and / or stop of the engine.

[0045] According to an advantageous embodiment, the VCR has a sensor unit for detecting a value indicating the presence and / or thickness of deposits in the upper range of the piston.

[0046] The deposits may cause wear steps that may lead to damage to the position ring.

[0047] The sensor unit may have an ultrasonic sensor. Alternatively, it may also include an optical sensor, or an electromagnetic sensor for detecting resistance or capacitance.

[0048] When the amount of sediment exceeds a predetermined limit value, it becomes necessary to remove the dirt.

[0049] The control unit can be adapted to cause piston movement at a temporary clearance position depending on the value detected by the sensor unit.

[0050] When a value corresponding to the limit value for the allowable amount of a predetermined sediment is detected by the sensor unit, the control unit can cause a change in the clearance position according to a scheme to reduce the sediment on the inner surface of the cylinder wall.

[0051] In an advantageous embodiment, the piston is connected to a piston rod and the piston comprises a setting unit for adjusting the compression ratio. Specifically, the setting unit has or is coupled to a mechanism for moving the top ring of the piston relative to the piston rod. It is preferred that the upper part of the piston where the top ring is mounted moves relative to the lower part of the piston and / or the piston rod.

[0052] The piston may have two or more parts movable relative to each other.

[0053] The control unit may have or be coupled to the same mechanism for moving the top ring of the piston relative to the piston rod, or may be coupled to another mechanism for adjusting the temporary clearance position.

[0054] The position of the top ring preferably defines the clearance position, and thus the clearance volume, together with the upper part of the piston. The length of the stroke, and thus the displacement volume, remains the same. Thus, the compression ratio can be changed by moving the top ring.

[0055] Alternatively, or in addition, the piston is connected to the crosshead via a piston rod, and the crosshead is connected to the crankshaft via a connecting rod to drive the crankshaft.

[0056] The crosshead can be provided with a mechanism for controlling the compression ratio. Specifically, the setting unit has or is coupled to a mechanism for moving the piston rod and / or the piston relative to the crosshead, such as that disclosed in European Patent No. 2687707 (A2).

[0057] The control unit may have or be coupled to the same mechanism for moving the piston rod and / or the piston relative to the crosshead, or may be coupled to another mechanism for adjusting the temporary clearance position.

[0058] Alternatively, or in addition, the connecting rod is provided with a mechanism for controlling the compression ratio. Specifically, the setting unit has or is coupled to a mechanism for moving the connecting rod relative to the crankshaft, such as that disclosed in European Patent 2801713 (A1). The mechanism can have an eccentric tappet at the bearing on the lower side of at least one connecting rod. The mechanism may further have a locking mechanism for fixing the eccentric tappet to either the connecting rod or the crank pin of the corresponding crankshaft in order to operate the reciprocating piston combustion engine in a changeable manner at each of the first or second compression ratios.

[0059] The control unit may have or be coupled to the same mechanism for moving the connecting rod relative to the crankshaft, or may be coupled to another mechanism for adjusting the temporary clearance position.

[0060] Alternatively, or in addition, the entire piston drive unit can be made movable so as to vary the gap position of the piston. The control unit and / or the setting unit may have or be coupled to a mechanism for moving the entire piston drive unit.

[0061] The present invention preferably relates to a large marine or shipboard engine, or a VCR internal combustion engine such as a stationary engine, the cylinder of which has an inner diameter of at least 200 mm. The engine is preferably a two-stroke engine or a two-stroke crosshead engine. The engine can be a diesel or gas engine, a dual-fuel or multi-fuel engine. In this type of engine, liquid and / or gaseous fuels can be combusted, and further, self-ignition or forced ignition is possible.

[0062] The engine has at least one cylinder that houses a piston. The piston is connected to a crankshaft. The piston reciprocates between the top dead center (TDC) and the bottom dead center (BDC) during the operation of the engine. Typically, the cylinder has at least one air passage opening for intake air, specifically an air inlet arranged in the liner of the cylinder, and at least one air passage opening for exhaust, specifically an exhaust outlet arranged in the cover of the cylinder.

[0063] The internal combustion engine can be a two-stroke engine that is scavenged longitudinally.

[0064] The term internal combustion engine also refers to large engines that can operate not only in diesel mode, which is characterized by self-ignition of fuel, but also in Otto mode, which is characterized by positive ignition of fuel, or in a mixed state of the two. Further, the term internal combustion engine includes, in particular, dual-fuel engines and large engines in which self-ignition of fuel is used for positive ignition of another fuel.

[0065] The rotational speed of the engine is preferably less than 800 RPM (four-stroke), and more preferably less than 200 RPM (two-stroke), which refers to the designation of a low-speed engine.

[0066] The fuel can be diesel or marine diesel oil, or heavy fuel oil, or emulsion, or slurry, or methanol, or ethanol, and gases such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), etc.

[0067] Furthermore, fuels that may be possible and can be added as required are: liquefied biogas (LBG), biofuels (e.g., algal fuels or seaweed oils), hydrogen, synthetic fuels made from CO2 (e.g., those made by power - to - gas or power - to - liquid).

[0068] The object of the present invention is also achieved by a method for the operation of a variable compression ratio (VCR) engine having at least one cylinder with a movable piston adapted to perform a predefined piston stroke within the cylinder. The method preferably comprises the steps of setting a predefined compression ratio by setting a predefined clearance position, preferably by a setting unit; setting at least one temporary clearance position different from the predefined clearance position, preferably by a control unit; and causing at least one piston movement at the temporary clearance position.

[0069] After setting the clearance positions, piston movements at the respective clearance positions, the respective clearance volumes, and the respective compression ratios are caused.

[0070] During the piston movement at the temporary clearance position, the fouling of the inner wall of the cylinder is removed in a range that cannot be reached by the piston movement at the predefined clearance position.

[0071] Finally, the piston movement is caused again at the predefined clearance position.

[0072] The piston movement at a temporary clearance position is preferably caused by at least one predetermined scheme. The scheme preferably defines a temporary clearance position, a time interval or number of strokes for maintaining the temporary clearance position, and / or successive values of a set period.

[0073] In particular, the scheme defines a stepwise increase and / or decrease of the temporary clearance position.

[0074] The piston movement at a temporary clearance position may be caused in response to a request, and / or after a predetermined number of piston strokes, and / or after a predetermined operating time.

[0075] For example, at least one piston movement at a temporary clearance position may be caused per 100 to 50,000,000 piston strokes, and / or per an operating time of 1 hour to 2 months.

[0076] For a VCR engine having at least two cylinders, the piston movement at a temporary compression ratio may be caused simultaneously for all cylinder pistons, or successively for each cylinder one by one, or simultaneously for some cylinders.

[0077] It is advantageous that the piston movement at a temporary clearance position is caused at each start and / or stop of the engine.

[0078] The clearance position can be adapted by moving the top ring of the piston, preferably the upper part of the piston having the top ring of the piston, relative to the lower part of the piston and / or the piston rod.

[0079] The clearance position can be adapted by moving the piston rod and / or the piston relative to the crosshead.

[0080] The clearance position can be adapted by moving the connecting rod relative to the crankshaft.

[0081] In an advantageous embodiment of the method, a value indicating the thickness of the sediment is detected, for example, by an ultrasonic sensor.

[0082] The piston movement at the temporary gap position is preferably caused depending on the value detected by the sensor unit.

[0083] The object of the present invention is achieved by a computer program product having a software code portion that can be directly read into the internal memory of a digital computer and that, when executed on a computer, performs the steps of the method according to the above. The scheme by which the piston movement is caused thereby may be stored in digital form in the memory.

Brief Description of the Drawings

[0084] The present invention will be further described below with reference to the drawings by way of examples.

Figure 1

Figure 2

Figure 3

Figure 4a

Figure 4b

Modes for Carrying Out the Invention

[0085] FIG. 1 shows a variable compression ratio (VCR) engine 1 having a cylinder 2 with a piston 3 movably disposed therein. The piston 3 is adapted to perform a predetermined piston stroke between top dead center and bottom dead center (not shown) within the cylinder 2. In the figure, the piston 3 is shown in an intermediate position.

[0086] The piston 3 is connected to the crosshead 7 via the piston rod 6, and the crosshead 7 is connected to the crankshaft 8 via the connecting rod 9 to drive the crankshaft 8.

[0087] The crosshead 7 is provided with a setting unit 4 for setting a preset compression ratio. The setting unit 4 has a mechanism for moving the piston rod 6 and the piston 3 relative to the crosshead 7.

[0088] When the piston rod 6 moves relative to the crosshead 7, the operating range of the piston 3 in the cylinder 2 changes, and the piston reaches a different top position (not shown) in the cylinder 2. Therefore, a new preset clearance position (see Figure 2) may be set by the control unit 4.

[0089] Furthermore, the VCR engine 1 has a control unit 5 for setting at least one temporary clearance position (see Figure 3) different from the preset clearance position 11 and causing piston movement at at least one temporary clearance position 15.

[0090] The control unit 5 is coupled to the setting unit 4. The mechanism 10 is used to adjust the preset clearance position and the temporary clearance position.

[0091] Alternatively, the control unit 5 may be coupled to another mechanism (not shown) for adapting the temporary clearance position.

[0092] Figure 2 shows a schematic view of the VCR engine 1 in which the piston 3 is at the preset clearance position 11.

[0093] The distance between the crosshead 7 and the piston 3 is set such that the piston 3 at the top position is well below the cylinder head 12. Therefore, there is a range 13 between the piston 3 and the cylinder head 12, where the inner wall 14 of the cylinder 2 is not peeled off by the piston 3. In this range 13, wear steps and carbonized deposits may occur.

[0094] The VCR mechanism 1 can have a sensor unit 16 for detecting the thickness of the deposit, for example an ultrasonic sensor.

[0095] If there is a layer of carbonized deposit that is thicker than a predetermined value, the control unit 5 can cause a temporary gap position to be set.

[0096] The gap position can be temporarily changed by the control unit 5 to a temporary gap position 15, for example as illustrated in Figure 3.

[0097] If the deposit is removed, the control unit 5 can return the gap position to the initial preset gap position 11.

[0098] Figure 4a shows a first typical curve chart of the gap position (CP) against time (t), where the gap position changes linearly from the preset gap position (PCP) to the temporary gap position (TCP). Figure 4b shows a second typical curve chart of the gap position (CP) against time (t), where the gap position changes stepwise.

[0099] The time (t) can be measured in time units or in the number of piston strokes.

[0100] The temporary gap position (TCP) can be held constant for a certain length of time tc.

[0101] Thereafter, the gap position is lowered linearly, for example as shown in Figure 4a, or stepwise, as shown in Figure 4b.

[0102] The gap position can return to the preset gap position (PCP) that was held before the increase, or to a different value, as indicated by the dotted line in Figure 4a. In this way, a new preset gap position can be selected.

[0103] Typically, the gap position can vary in the range from 20 to 200 mm.

Claims

1. at least one cylinder (2) having a piston (3) movably disposed within said cylinder (2), said piston (3) adapted to perform a predetermined piston stroke within said cylinder (2); a setting unit (4) for setting a preset compression ratio by setting a preset gap position (11); A variable compression ratio (VCR) engine (1) having 1. A variable compression ratio (VCR) engine (1), characterized in that the VCR engine (1) further comprises a control unit (5) for setting at least one temporary gap position (15) different from the preset gap position (11) and for causing at least one piston movement at the temporary gap position (15).

2. 2. A variable compression ratio (VCR) engine according to claim 1, wherein the control unit (5) is adapted to cause at least one piston movement in a temporary gap position (15) according to at least one predefined scheme, said scheme preferably defining successive values ​​of the temporary gap position (15), a time interval for holding the temporary gap position (15) and / or a set period.

3. The control unit (5) controls the piston movement at the temporary clearance position (15). Upon request, and / or Every 100 to 5,000,000 piston strokes, and / or For every 1 hour to 2 months of driving time, A variable compression ratio (VCR) engine according to claim 1 or 2, adapted to cause

4. the VCR engine (1) having at least two cylinders (2), the control unit (5) being adapted to cause piston movement at a temporary clearance position (15) for a selected cylinder, Or, said VCR engine (1) having at least two cylinders (2), said control unit (5) being adapted to trigger piston movements in a temporary clearance position (15) for all cylinder pistons (3) simultaneously or one cylinder (2) at a time, Or, 4. A variable compression ratio (VCR) engine according to claim 1, wherein the VCR engine (1) has a number of installed cylinders (2), the number of which is at least three, and the control unit (5) is adapted to simultaneously cause piston movement in a temporary clearance position (15) for a number of cylinders (2) ranging from two to the number of installed cylinders minus one.

5. 5. A variable compression ratio (VCR) engine according to any one of claims 1 to 4, wherein the control unit (5) is adapted to cause piston operation in a temporary clearance position (15), preferably at maximum compression ratio, at each start and / or stop of the engine.

6. 6. A variable compression ratio (VCR) engine according to claim 1, wherein the VCR engine (1) comprises a sensor unit (16), for example an ultrasonic sensor, for detecting a value giving an indication of the thickness of the deposit.

7. 7. A variable compression ratio (VCR) engine according to claim 6, wherein the control unit is adapted to cause piston operation at a temporary clearance position (15) based on the value detected by the sensor unit (16).

8. said piston (3) being connected to a piston rod (6) and said piston (3) being connected to said setting unit (4) for controlling said compression ratio, said piston (3) in particular having a mechanism for moving a top ring of said piston (3) relative to said piston rod (6); and / or the pistons (3) are connected via piston rods (6) to a crosshead (7), the crosshead (7) is connected via connecting rods (9) to a crankshaft (8) for driving the crankshaft (8), and the crosshead (7) is connected to the setting unit (4) for controlling the compression ratio, the crosshead (7) comprising in particular a mechanism (10) for moving the piston rods (6) and / or the pistons (3) relative to the crosshead (7), and / or 8. A variable compression ratio (VCR) engine according to claim 1, wherein the pistons (3) are connected via piston rods (6) to a crosshead (7), the crosshead (7) is connected via a connecting rod (9) to a crankshaft (8) to drive the crankshaft (8), and the connecting rod (9) is connected to the setting unit (4) for controlling the compression ratio, the connecting rod (9) in particular having a mechanism for moving the connecting rod (6) relative to the crankshaft (8), such as an eccentric tappet at a lower bearing of the at least one connecting rod, and a fixing mechanism for fixing the eccentric tappet either to the connecting rod or to a corresponding crank pin of the crankshaft in order to variably operate the VCR engine at a first or a second compression ratio, respectively.

9. 9. A variable compression ratio (VCR) engine according to any one of claims 1 to 8, wherein the VCR engine (1) is a marine engine with at least one cylinder having an inner diameter of at least 200 mm, preferably a two-stroke engine or a two-stroke crosshead engine, more preferably a dual or multi-fuel engine.

10. 1. A method for operating a variable compression ratio (VCR) engine having at least one cylinder (2) with a movable piston (3), said piston (3) adapted to perform a predetermined piston stroke within said cylinder (2), comprising the steps of: setting a preset compression ratio by setting a preset gap position (11); setting at least one temporary gap position (15) different from said preset gap positions (11); causing at least one piston movement at said temporary clearance position (15); The method includes:

11. 11. The method according to claim 10, wherein the piston movement at the temporary gap position is triggered according to at least one predefined scheme, said scheme preferably defining successive values ​​of temporary gap positions, time intervals for holding the temporary gap positions (15) and / or set periods.

12. The piston movement in the temporary clearance position (15) Upon request, and / or Every 100 to 5,000,000 piston strokes, and / or Every 1 hour to 2 months of driving time The method according to claim 10 or 11, wherein the

13. The VCR engine has at least two cylinders (2), and the piston movement at the temporary clearance position is Simultaneously for all cylinders and pistons Or, One cylinder at a time, Or, Simultaneously, a part of the cylinder (2) The method according to claims 10 to 12, wherein

14. 14. The method according to any one of claims 11 to 13, wherein the piston movement in a temporary clearance position (15) is caused at each start and / or stop of the engine.

15. The gap position is moving a top ring of the piston relative to a piston rod; and / or Moving the piston rod and / or the piston relative to the crosshead; and / or To move the connecting rod relative to the crankshaft 15. The method according to any one of claims 11 to 14, wherein the method is adapted by:

16. A computer program product directly readable into the internal memory of a digital computer, comprising software code portions for carrying out the steps of the method according to any one of claims 10 to 15 when said product is executed on a computer.

Images