Variable Compression Ratio (VCR) Engine

Abstract

Provide a variable compression ratio (VCR) engine with better performance and lower maintenance requirements than the prior art. 【Solution】The variable compression ratio (VCR) engine 1 includes at least one cylinder 2 equipped with a piston 3 movably disposed therein and adapted to perform a predetermined piston stroke, and a setting unit 4 that sets a preset compression ratio by setting a preset clearance position. The VCR engine 1 further includes a control unit 5 that sets at least one temporary clearance position different from the preset clearance position and causes at least one piston operation at the temporary clearance position.

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. 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 within 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 change.

[0009] In a combustion engine, during long-term operation, carbon may deposit 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 varying 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 top 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 that the piston, piston rings, and cylinder liners may be damaged. In a variable compression ratio (VCR) engine, to ensure the reliability of engine operation, management of carbon deposition and avoidance of wear steps are essential.

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 and a method of operating a variable compression ratio (VCR) engine that avoid the drawbacks of the prior art and, in particular, have more sustainable performance and lower maintenance requirements than prior art engines.

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 of 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 arranged within the cylinder and adapted to perform a predefined piston stroke within the cylinder. The variable compression ratio (VCR) engine has a setting unit for setting a predefined compression ratio by setting a predefined 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, which 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 predefined clearance position is the uppermost position of the piston to be predefined, in particular the uppermost position of the top ring, and corresponds to the respective clearance volume.

[0021] The top ring is a sealing ring arranged 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 in most cases not be changed. Therefore, the setting of the clearance volume defines the compression ratio.

[0023] Normally, within the cylinder there is the highest uppermost position reachable by the piston, which position corresponds to the smallest achievable clearance volume and the highest 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 then preferably re-sets the preset clearance position and adapts to cause 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, especially when the top ring of the piston passes through this range, may be removed.

[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 value 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 that defines 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 step - by - step 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 with wear steps, 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 throughout the 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 piston movement at a temporary clearance position at least once per 100 to 5,000,000 piston strokes.

[0039] Alternatively, or in addition, the control unit is adapted to cause piston movement at a temporary clearance position at least once 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 predetermined piston stroke at a preset clearance position to provide a predetermined combustion, a predetermined thermal efficiency, and a predetermined 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 by one for each cylinder.

[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 predetermined 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 result in 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 gap 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 gap 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 preferable 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 gap position.

[0054] The position of the top ring preferably defines the gap position, and thus the gap 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, driving 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 on the bearing below 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 operably change the reciprocating piston combustion engine 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 ship engine, or a VCR internal combustion engine such as a stationary engine, in which the cylinder 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 fuel 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 top dead center (TDC) and 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 characterized by self-ignition of fuel, but also in Otto mode 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 title 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] Further possible fuels that 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 predetermined piston stroke within the cylinder. The method preferably comprises the steps of setting a preset compression ratio by setting a preset clearance position, preferably by a setting unit, and setting at least one temporary clearance position different from the preset clearance position, preferably by a control unit, and causing at least one piston movement at the temporary clearance position.

[0069] After setting the clearance position, piston movements are caused at each clearance position, each clearance volume, and each compression ratio.

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

[0071] Finally, the piston movement is again caused at the preset 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 if 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 a beneficial embodiment of the method, a value giving an indication of the sediment thickness is detected, for example, by an ultrasonic sensor.

[0082] The piston movement at the temporary clearance 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 loaded 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 digitally in the memory.

Brief Description of the Drawings

[0084] The present invention will be further described below with reference to the drawings in embodiments.

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 the top dead center and the bottom dead center (not shown) in 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, there may be wear steps and carbonized deposits.

[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 diagram 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 diagram 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 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), the temporary gap position being above the preset gap position, the control unit (5) being adapted to cause the piston movement at the temporary gap position (15) according to at least one predefined scheme, the scheme defining successive values ​​of a plurality of temporary gap positions (15), and the scheme defining a stepwise increase and / or decrease of the plurality of temporary gap positions, The control unit (5) controls the piston movement at the temporary clearance position (15). Every 100-5,000,000 piston strokes, and on demand, or Every hour to two months of operation, and on demand. A variable compression ratio (VCR) engine (1) adapted to cause

2. 2. A variable compression ratio (VCR) engine according to claim 1, wherein the scheme provides a curve defining the temporary gap position versus time or versus number of piston strokes, whereby the temporary gap position is variable according to the curve versus time or versus number of piston strokes, and / or the scheme defines a number of strokes during which a temporary gap position (15) is held.

3. 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, 3. A variable compression ratio (VCR) engine according to claim 1 or 2, 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.

4. 4. A variable compression ratio (VCR) engine according to any one of claims 1 to 3, wherein the control unit (5) is adapted to cause piston operation in a temporary clearance position (15) at each start and / or stop of the engine.

5. 5. A variable compression ratio (VCR) engine according to any one of claims 1 to 4, characterized in that the VCR engine (1) comprises a sensor unit (16) for detecting a value giving an indication of the thickness of the deposit.

6. 6. A variable compression ratio (VCR) engine according to claim 5, wherein the control unit is adapted to cause a piston operation at a temporary clearance position (15) based on the value detected by the sensor unit (16).

7. said piston (3) being connected to a piston rod (6) and said piston (3) being connected to said setting unit (4) for controlling said preset 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 said pistons (3) being connected via piston rods (6) to a crosshead (7), said crosshead (7) being connected via connecting rods (9) to a crankshaft (8) for driving said crankshaft (8), said crosshead (7) being connected to said setting unit (4) for controlling said preset compression ratio, said crosshead (7) in particular comprising a mechanism (10) for moving said piston rods (6) and / or said pistons (3) relative to said crosshead (7), and / or 7. A variable compression ratio (VCR) engine according to any one of claims 1 to 6, characterized in that the pistons (3) are connected via piston rods (6) to a crosshead (7), the crosshead (7) being connected via connecting rods (9) to a crankshaft (8) for driving the crankshaft (8), the connecting rods (9) being connected to the setting unit (4) for controlling the pre-set compression ratio, the connecting rods (9) in particular having a mechanism for moving the connecting rods (6) relative to the crankshaft (8).

8. 8. A variable compression ratio (VCR) engine according to any one of claims 1 to 7, wherein the VCR engine (1) is a marine engine, i.e. a two-stroke engine or a two-stroke crosshead engine, with at least one cylinder having an inner diameter of at least 200 mm.

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

10. A variable compression ratio (VCR) engine according to claim 5, wherein said sensor unit (16) is an ultrasonic sensor.

11. A variable compression ratio (VCR) engine according to claim 8, wherein the VCR engine (1) is a dual or multi-fuel engine.

12. 8. A variable compression ratio (VCR) engine according to claim 7, wherein the mechanism for moving the connecting rod (6) relative to the crankshaft (8) comprises an eccentric tappet at a lower bearing of the at least one connecting rod and a fixing mechanism for fixing the eccentric tappet to either the connecting rod or a corresponding crank pin of the crankshaft for variably operating the VCR engine at each of a first or second compression ratio.

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