EP4086443A1

EP4086443A1 - An internal combustion engine and a method of operating the internal combustion engine

Info

Publication number: EP4086443A1
Application number: EP21172304.4A
Authority: EP
Inventors: Lambertus Hendrik De Gooijer
Original assignee: Gomecsys BV
Current assignee: Gomecsys BV
Priority date: 2021-05-05
Filing date: 2021-05-05
Publication date: 2022-11-09
Also published as: WO2022233690A1

Abstract

An internal combustion engine (1) comprises an oil pump (35), an oil line (22) being fluidly connected to the oil pump (35) and engine parts to be lubricated and a hydraulic actuator (18) including an actuator housing which accommodates a movable plunger (19) and an oil chamber (20). The plunger (19) is drivably coupled to an adjusting element (17) for adjusting an engine operating mode. The engine (1) is provided with a control system (CS) including a first control mode for moving the plunger (19) in a first direction (X), a second control mode for moving the plunger (19) in a second direction (Y) which is opposite to the first direction (X) and a third control mode for maintaining the plunger (19) at a fixed position within the actuator housing. The engine (1) is provided with a first passage (27) in the oil line (22) and a second passage (28) between the oil line (22) at an upstream side of the first passage (27) and the oil chamber (20). The first passage (27) is closable by the control system (CS), wherein the control system (CS) is configured such that under operating conditions in the first control mode the first passage (27) is closed such that the oil pump (35) communicates with the oil chamber (20) only.

Description

The present invention relates to an internal combustion engine, comprising an oil pump, an oil line being fluidly connected to the oil pump and engine parts to be lubricated and a hydraulic actuator including an actuator housing which accommodates a movable plunger and an oil chamber, which plunger is drivably coupled to an adjusting element for adjusting an engine operating mode, wherein the engine is provided with a control system including a first control mode for moving the plunger in a first direction, a second control mode for moving the plunger in a second direction which is opposite to the first direction and a third control mode for maintaining the plunger at a fixed position within the actuator housing.
Such an internal combustion engine is known from WO 2015/121254 . The adjustable engine operating mode of the known internal combustion engine is its compression ratio. The adjusting element for varying the compression ratio is in the form of a control shaft which is drivably coupled to the plunger of the hydraulic actuator.
The present invention aims to provide an internal combustion engine including a low-cost solution for adjusting an engine operating mode.
For this purpose the internal combustion engine according to the invention is characterized in that the engine is provided with a first passage in the oil line and a second passage between the oil line at an upstream side of the first passage and the oil chamber, which first passage is closable by the control system, wherein the control system is configured such that under operating conditions in the first control mode the first passage is closed such that the oil pump communicates with the oil chamber only.
An advantage of the invention is that the oil pump, which is usually necessary in an internal combustion engine for lubricating engine parts is also used for adjusting an engine operating mode, whereas the oil pump may operate at a relative low pressure under certain operating conditions during which an adjustment of the engine operating mode is not required. In the latter situation, i.e. the third control mode, the first passage is open such that oil directly flows from the oil pump to the engine parts to be lubricated and the plunger of the hydraulic actuator remains in the same position within the actuator housing.
Since in the first control mode the first passage is closed, a direct oil flow from the oil pump to the engine parts to be lubricated is obstructed and the oil pump communicates with the oil chamber only. Consequently, pressure in the oil chamber will rise and the plunger of the hydraulic actuator will be moved in the first direction. In practice, the first control mode may be a relatively short period, depending on a counter force on the plunger and the speed of pressure build-up by the oil pump when the first passage is closed. A short temporary interruption of oil flow to the engine parts to be lubricated may be allowable.
The invention provides a low-cost solution for engines in which the oil pump usually has a relatively low output pressure, such as in certain motorbikes. The usual output pressure for lubricating engine parts may be about 1 bar, for example. Such a pressure level may be too low to move the plunger, but by closing the first passage as described above the output pressure of the oil pump will automatically increase immediately during driving the oil pump and push the plunger in the first direction. In practice, excessive oil pressure in the oil line may be avoided by applying a pressure relief valve.
In an embodiment the oil chamber is a first oil chamber and the actuator housing accommodates a second oil chamber wherein the first and second oil chambers are located at respective opposite sides of the plunger and the second oil chamber communicates with a third passage. In the first control mode, when the plunger moves in the first direction, it can push oil from the second oil chamber to the third passage.
In an embodiment the third passage is provided between the oil line at a downstream side of the first passage and the second oil chamber such that in the first control mode the third passage allows oil to flow from the second oil chamber to the engine parts to be lubricated. Hence, when the plunger is moved in the first direction it forces oil from the second oil chamber via the third passage to the oil line at the downstream side of the first passage to the engine parts to be lubricated. This means that oil flow to the engine parts to be lubricated continues in the first control mode such that interruption of oil flow to the engine parts is minimized.
The third passage may be closable by the control system, wherein the control system is configured such that under operating conditions in the first control mode the third passage is open such that oil flow to the engine parts to be lubricated continues. In the third control mode the third passage may be closed.
In a particular embodiment the engine comprises a mechanical power source which is drivably coupled to the adjusting element such that under operating conditions the adjusting element transfers a force from the mechanical power source to the plunger in the second direction. This means that in the first control mode the plunger must be moved against the force from the mechanical power source to the plunger.
In an embodiment the second passage is closable by the control system and the oil chamber communicates with an oil drain line for discharging oil from the oil chamber which oil drain line is closable by the control system, wherein the control system is configured such that under operating conditions in the first control mode the second passage is open and the oil drain line is closed and in the second control mode at least one of the second passage and the oil drain passage is open. Hence, in the first control mode the oil chamber communicates with the oil pump only, whereas in the second control mode the plunger pushes oil from the oil chamber through at least one of the oil drain line and the second passage, for example caused by the mechanical power source that moves the plunger in the second direction in case of the presence of a mechanical power source that is drivably coupled to the adjusting element. The first passage may be open or closed in the second control mode. The oil drain line may be fluidly connected to the oil line, for example downstream of the first passage. If in the latter case the second passage is closed and the oil drain line and the first passage are open in the second control mode the oil flows from the oil chamber through the oil drain line to the oil line. The second passage may be closable by a one-way valve which allows oil flow towards the oil chamber only, such that in the first control mode oil can flow to the oil chamber and in the second control mode the second passage is closed, whereas the oil drain line is open. This means that the mechanical power source may move the plunger in the second direction if oil can flow away from the oil chamber through the oil drain line, or if oil can flow away from the first oil chamber through the oil drain line in case of a first and second oil chamber. In the first control mode the oil drain line is closed.
In a compact embodiment the oil drain line is incorporated in the closable second passage, wherein the control system is configured such that under operating conditions in the first control mode the second passage is open and in the second control mode the first and second passages are open. This means that in the second control mode oil flows directly from the oil pump to the engine parts to be lubricated without building-up significant pressure in the first oil chamber to move the plunger. If the above-mentioned mechanical power source is present the plunger may be mainly or entirely moved by the mechanical power source in the second control mode. During such a movement the plunger transfers oil from the oil chamber through the second passage to the oil line.
Alternatively, the engine may be provided with a bypass between the first and second oil chambers, which bypass is closable by the control system, wherein the control system is configured such that under operating conditions in the first control mode the bypass is closed and in the second control mode the bypass is open. In the second control mode the first passage may be open, whereas the second passage may be closed if the second passage is closable. If the third passage is also closable by the control system, the control system may be configured such that under operating conditions in the first control mode the third passage is open; furthermore, the control system may be configured such that under operating conditions in the second control mode the third passage is closed. In the latter case the plunger may transfer oil from the first oil chamber to the second oil chamber via the bypass. If in that case the second passage is closable and the second passage is also closed in the second control mode the plunger may transfer oil from the first oil chamber to the second oil chamber via the bypass only. In a further embodiment the third passage may be incorporated in the bypass.
The bypass may be provided with a check valve which allows oil flow from the first to the second oil chamber only. This prevents the plunger from being moved in the first direction during the second control mode when the mechanical power source temporarily exerts a force on the plunger in the first direction in case of the presence of a mechanical power source that is drivably coupled to the adjusting element.
If the second passage is closable by the control system the control system may be configured such that under operating conditions in the third control mode the first passage is open and the second passage is closed so as to maintain the plunger at a fixed position within the actuator housing. If the second passage would not be closable or if the second passage would be open in the third control mode there may be a holding force on the plunger to keep the plunger at the fixed position within the actuator housing, for example a friction force.
When the third passage is present, the third passage may also be closable by the control system and the control system may be configured such that under operating conditions in the third control mode the third passage is closed.
In case of the presence of a bypass as described hereinbefore, the control system may be configured such that under operating conditions in the third control mode the bypass is closed.
In an alternative embodiment the engine is provided with a fourth passage between the oil line at an upstream side of the first passage and the second oil chamber, and a fifth passage between the oil line at a downstream side of the first passage and the first oil chamber, wherein the second, third, fourth and fifth passages are closable by the control system, wherein the control system is configured such that under operating conditions in the second control mode the first, second and third passages are closed and the fourth and fifth passages are open, and in the first control mode the second and third passages are open and the fourth and the fifth passages are closed. Since in this case in the second control mode the first passage is closed a direct oil flow from the oil pump to the engine parts to be lubricated is obstructed and the oil pump communicates with the second oil chamber only so as to move the plunger in the second direction. If the engine comprises a mechanical power source which is drivably coupled to the adjusting element such that under operating conditions the adjusting element transfers a force from the mechanical power source to the plunger in the second direction, the plunger is moved in the second direction by both the mechanical power source and the oil pump in the second control mode.
The control system may be configured such that under operating conditions in the third control mode the first passage is open. Preferably, the second, third, fourth and fifth passages are closed so as to maintain the plunger at a fixed position within the actuator housing.
In a practical embodiment the engine has at least a crankcase, a piston, a connecting rod, a crankshaft that is rotatably mounted to the crankcase and a control mechanism for adjusting the compression ratio of the engine, to which control mechanism the adjusting element is drivably coupled, wherein the mechanical power source is formed by at least one of the piston, the connecting rod and the control mechanism exerting a force on the adjusting element under operating conditions. The piston, the connecting rod and the control mechanism cooperate with each other. For example, under operating conditions repetitive combustion forces on the piston may be transferred through the connecting rod, the control mechanism and the adjusting element to the plunger and create an average force on the plunger in the second direction.
In a particular embodiment the control mechanism comprises an eccentric member which is rotatably mounted on a crankpin of the crankshaft, the connecting rod is rotatably mounted on the eccentric member and the adjusting element comprises a control shaft which extends through the crankshaft and which is rotatable with respect to the crankshaft about the crankshaft axis, wherein the eccentric member is drivably coupled to the control shaft through a transmission, which is adapted such that under operating conditions the eccentric member rotates about the crankpin at half speed of the crankshaft, when the control shaft has a fixed rotational position with respect to the crankcase. More particularly, the transmission may be adapted such that under operating conditions the eccentric member rotates about the crankpin at half speed of the crankshaft and in opposite direction thereof, when the control shaft has a fixed rotational position with respect to the crankcase. The transmission may comprise a gear transmission.
It is noted that there may be some leakage along the plunger from the oil chamber or between the first and second oil chambers. This may even be desired, for example in case of the embodiment in which the transmission comprises a gear transmission. In that case the plunger will automatically shift away from a steady-state setpoint in the third control mode due to the leakage such that the compression ratio will automatically shift. This means that repetitive contact locations between engaging gears will slightly shift with respect to each other, hence improving durability of the gears. The control system may be configured such that after a certain shift it switches to the first or second control mode in order to return to the original setpoint.
The plunger may be rotatable within the actuator housing. In this case the control shaft can be directly coupled to the plunger, for example.
The invention is also related to a method of operating the internal combustion engine as described hereinbefore, wherein at least in one of the first and second oil chambers, or the oil chamber, the actual pressure is measured, on the basis of which the compression ratio is adjusted when the actual pressure at a certain engine operating point differs from a desired pressure at the engine operating point by adjusting the position of the adjusting element towards a position where the difference decreases. This method may be performed during the third mode when the first passage is open and the second passage is closed, for example, in which case the plunger has a fixed position within the actuator housing and the mechanical power source on the plunger may create different pressures in the first and second oil chambers, respectively. The actual pressures in the first and second oil chambers depend on the combustion pressure at each engine operating point. If the actual pressure in the first or second oil chamber at an engine operating point is different from the pressure which may be expected at that operating point, i.e. the desired pressure, this may be an indication that the actual compression ratio is different from the desired compression ratio at that operating point. An engine management system of the internal combustion engine may then change the position of the adjusting element towards a position where the difference decreases via the first or second control mode, such that the compression ratio comes closer to the desired compression ratio. The relationship between the desired pressure in at least one of the first and second oil chambers, i.e. the desired compression ratio, and the engine operating points may be contained in a look-up table in the engine management system.
The engine operating point may be defined by engine speed and load.
The invention will hereafter be elucidated with reference to the schematic drawings showing embodiments of the invention by way of example.

Fig. 1 is a perspective view of a part of an embodiment of an internal combustion engine according to the invention.
Fig. 2 is a similar view as Fig. 1, showing a part thereof on a larger scale and seen from a different side.
Fig. 3 is an illustrative view of the internal combustion engine as shown in Fig. 1.
Fig. 4 is a perspective view of a part of a hydraulic actuator of the internal combustion as shown in Fig. 1.
Figs. 5-7 are illustrative views of a part of the internal combustion engine of Fig. 1, illustrating three different control modes of a control system of the internal combustion engine as shown in Fig. 1.
Figs. 8-10 are enlarged parts of Figs. 5-7, respectively, illustrating the control modes in a different way.
Fig. 11 is a similar view as Fig. 9 on a larger scale, but showing the control mode in an alternative embodiment of the internal combustion engine.
Fig. 12 is a similar view as Fig. 11, but showing another alternative embodiment.
Figs. 13-15 are similar views as Figs. 5-7, but showing still another alternative embodiment.

Figs. 1 and 2 show details of a part of an embodiment of an internal combustion engine 1 according to the invention. The engine 1 is a four-stroke engine and has a variable compression ratio which provides the opportunity to operate the engine at high compression ratio under part-load conditions resulting in improved efficiency. Under high-load conditions the compression ratio can be lowered in order to avoid knocking. The engine 1 comprises a crankcase 2, which supports a crankshaft 3 by crankshaft bearings. The crankshaft 3 has a crankshaft axis 4 and is rotatable with respect to the crankcase 2 about the crankshaft axis 4.
The crankshaft 3 comprises a central main portion 5, a crankpin 6 including a crankpin axis and a crankshaft web 7. The crankshaft web 7 is located between the central main portion 5 and the crankpin 6. It is noted that in Figs. 1 and 2 a front side of the engine 1 is located at the right side in the drawings. Thus, the central main portion 5 projects from the crankcase 2 at the front side of the engine 1. At the opposite rear side of the engine 1 a flywheel (not shown) is fixed to the crankshaft 3.
The engine 1 comprises an eccentric member 8 which is rotatably mounted on the crankpin 6. The eccentric member 8 is provided with a bearing portion 9 which is disposed eccentrically with respect to the crankpin 6. The bearing portion 9 has an outer circumferential surface which bears a big end 10 of a connecting rod 11. Thus, the connecting rod 11 is rotatably mounted on the eccentric member 8 via its big end 10. The connecting rod 11 also includes a small end 12 to which a piston 13 is rotatably connected through a piston pin.
The eccentric member 8 is provided with an external eccentric member gear 14 which meshes with two external intermediate gears 15. The intermediate gears 15 are rotatably mounted to the crankshaft 3 and their axes of rotation extend parallel to the crankshaft axis 4. Each of the intermediate gears 15 also meshes with an external control shaft gear 16, which is fixed to a control shaft 17. The control shaft 17 extends concentrically through the central main portion 5 of the crankshaft 3 and projects from the central main portion 5 as seen from the crankpin 6. The control shaft 17 is rotatable with respect to the crankshaft 3 about the crankshaft axis 4. Thus, the control shaft 17 is rotatable about a control shaft axis which coincides with the crankshaft axis 4. Similarly, the centre line of the control shaft gear 16 also coincides with the crankshaft axis 4.
The eccentric member gear 14, the intermediate gears 15 and the control shaft gear 16 together form a transmission between the control shaft 17 and the eccentric member 8 at a side of the crankshaft web 7 where the crankpin 6 is located. The mentioned gears 14 - 16 are arranged and dimensioned such that under operating conditions the eccentric member 8 rotates about the crankpin 6 at half speed of the crankshaft 3 and in opposite direction thereof, when the control shaft 17 has a fixed rotational position with respect to the crankcase 2. A different transmission which causes the eccentric member 8 to rotate about the crankpin 6 at half speed of the crankshaft under operating is conceivable, when the control shaft 17 has a fixed rotational position with respect to the crankcase 2.
It is noted that Fig. 1 only shows one piston 13 and corresponding crankpin 6 and eccentric member 8, but the engine 1 may be a multi-cylinder engine including a plurality of crankpins and associated eccentric members, in which the eccentric members are mutually coupled in order to achieve similar rotational movements of the respective eccentric members with respect to the crankcase 2.
Under operating conditions of the engine 1 the eccentric member 8 can be rotated with respect to the crankpin 6 at a virtual standstill of the crankshaft 3 by means of adjusting the rotational position of the control shaft 17 with respect to the crankcase 2. This provides the opportunity to change top dead centre of the reciprocating piston 13 at compression strokes of the piston 13, i.e. to vary the compression ratio of the engine 1.
Fig. 3 shows a momentary condition of the internal combustion engine 1 schematically, in which E = maximum eccentricity of the bearing portion 9 of the eccentric member 8, α1 = angle between a plane spanned by a centreline of the piston pin and the crankshaft axis 4 and a plane spanned by the centreline of the piston pin and a centreline of the bearing portion 9, α2 = angle between the plane spanned by the centreline of the piston pin and the centreline of the bearing portion 9 and a plane spanned by the centreline of the bearing portion 9 and the crankpin axis, and α3 = angle between a plane spanned by the centreline of the piston pin and the crankshaft axis 4 and a plane spanned by the crankpin axis and the crankshaft axis 4. The positions of the connecting rod 11, the maximum eccentricity E of the bearing portion 9 and the crankshaft 3 in the momentary condition as shown in Fig. 3 are such that if a combustion force is exerted on the piston 13 this force will be transferred via the connecting rod 11 to the eccentric member 8 and generate a torque on the eccentric member 8 about the centreline of the crankpin 6. This torque will be transferred by the eccentric member gear 14, the intermediate gears 15 and the control shaft gear 16 to the control shaft 17. Hence, if under operating conditions the control shaft 17 is not hold at a fixed position with respect to the crankcase 2 it may be rotated automatically.
It is noted that other forces than the combustion force may generate a torque on the control shaft 17, for example inertia forces of at least one of the piston 13, the connecting rod 11 and the eccentric member 8.
The direction of the torque exerted on the control shaft 17 may vary, for example depending on the momentary mutual positions of the piston 13, connecting rod 11, eccentric member 8 and crankshaft 11, but in general an average torque on the control shaft 17 is directed in one direction only.
The functioning of the mechanical structure of the internal combustion engine 1 including variable compression ratio as shown in Figs. 1-3 is also described in WO 2013/110700 , but numerous alternative engine types including variable compression ratio in which forces from the piston and/or the connecting rod exert a torque on the control shaft are conceivable.
According to the present invention the internal combustion engine 1 is provided with a hydraulic actuator 18, of which an interior is shown in Fig. 4. The hydraulic actuator 18 comprises an actuator housing which accommodates a movable plunger 19, a first oil chamber 20 and a second oil chamber 21. The plunger 19 divides an interior space of the actuator housing into the first oil chamber 20 and the second oil chamber 21, such that opposite sides of the plunger 19 contact the first and second oil chambers 20, 21. A free end of the plunger 19 is slidable along an inner ring portion of the actuator housing. The plunger 19 is drivably coupled to the control shaft 17, for example directly such that an axis of rotation of the plunger 19 coincides with the crankshaft axis 4. In this embodiment the control shaft 17 forms an adjusting element for adjusting an engine operating mode according to the invention, more specifically an engine operating mode in the form of compression ratio.
The engine 1 is provided with a control system CS that has three different control modes, which are illustrated in Figs. 5-7: a first control mode for moving the plunger 19 in a first rotational direction X, Fig. 7, a second control mode for moving the plunger 19 in a second rotational direction Y which is opposite to the first rotational direction X, Fig. 6, and a third control mode for maintaining the plunger at a fixed position within the actuator housing, Fig. 5. In this case the first rotational direction X is anticlockwise and the second rotational direction Y is clockwise.
Figs. 5-7 also show an oil pump 35, an oil filter 36 and an oil line 22. The oil line 22 is fluidly connected to engine parts to be lubricated (not shown) and to the oil pump 35. The oil pump 35, oil filter 36 and oil line 22 may be well known components which are applied in most internal combustion engines. Figs. 5-7 show that the engine 1 is provided with a hydraulic control unit 23 which comprises a hydraulic housing 24, a first hydraulic valve 25 and a second hydraulic valve 26. The first and second hydraulic valves 25, 26 are movable independently from each other with respect to the hydraulic housing 24 by the control system CS.
The hydraulic housing 24 is provided with oil channels which cooperate with the first and second hydraulic valves 25, 26 such that three different oil flow directions can be created for the three control modes by selecting different positions of the first and second hydraulic valves 25, 26. This is illustrated in Figs. 8-10, which show the same positions of the first and second hydraulic valves 25, 26 as shown in Figs. 5-7, respectively. Fig. 8 shows a closable first passage 27 which is located in the oil line 22. Fig. 10 shows a closable second passage 28 between the oil line 22 at an upstream side of the first passage 27 and the first oil chamber 20, and a closable third passage 29 between the oil line 22 at a downstream side of the first passage 27 and the second oil chamber 21. Fig. 9 shows a closable fourth passage 30 between the oil line 22 at an upstream side of the first passage 27 and the second oil chamber 21 and a closable fifth passage 31 between the oil line 22 at a downstream side of the first passage 27 and the first oil chamber 20.
The control system CS is configured such that under operating conditions in the first control mode the first passage 27 is closed, the second and third passages 28, 29 are open so as to move the plunger 19 in the first rotational direction X, whereas the fourth and fifth passages 30, 31 are closed. This is illustrated in Fig. 10. The control system CS is configured such that under operating conditions in the second control mode the first, second and third passages 27, 28, 29 are closed and the fourth and fifth passages 30, 31 are open so as to move the plunger 19 in the second rotational direction Y. This is illustrated in Fig. 9. The control system CS is configured such that under operating conditions in the third control mode the first passage 27 is open and the second to fifth passages 28-31 are closed so as to keep the position of the plunger 19 at a fixed location with respect to the actuator housing. This is illustrated in Fig. 8.
In the third control mode oil flows from the oil pump 35 through the first passage 27 to the engine parts to be lubricated, similar to conventional internal combustion engines. In the first control mode the oil pump 35 is fluidly connected to the first oil chamber 20 only via the second passage 28. Due to obstruction of the oil flow the pressure output of the oil pump 35 will rise and the plunger 19 will be rotated in the first rotational direction X. Simultaneously, the plunger 19 will generate oil flow from the second oil chamber 21 through the third passage 29 to the engine parts to be lubricated. A similar effect occurs in the second control mode. This means that in the first and second control modes oil flow to the engine parts to be lubricated continues.
Since in the embodiment as shown in Figs. 1-10 the control shaft 17 is drivably coupled to the plunger 19 the piston 13 and/or the connecting rod 11 and/or the eccentric member 8 form a mechanical power source which exert a torque onto the plunger 19 under operating conditions as described hereinbefore in relation to Fig. 3. For example, if in the situations as shown in Figs. 8-10 the average torque on the plunger 19 is directed clockwise, in the third control mode as shown in Fig. 8 the pressure in the first oil chamber 20 will be higher than in the second oil chamber 21, but the plunger 19 will not be rotated. In the second control mode as shown in Fig. 9 the torque on the plunger 19 will support the oil pump 35 in moving the plunger 19 in the second rotational direction Y. In the first control mode as shown in Fig. 10 the oil pump 35 must provide more power to move the plunger 19 in the second rotational direction Y against the torque on the plunger 19.
In practice the torque on the plunger 19 may be at such a level that in the second control mode the power of the oil pump is not necessary to move the plunger 19 in the second rotational direction Y. In that case the fourth and fifth passages 30, 31 as illustrated in Fig. 9 may be omitted and the hydraulic housing 24 may be provided with a closable bypass 32 between the first and second oil chambers 20, 21. This is illustrated in Fig. 11 which shows a part of an alternative embodiment of the internal combustion engine 1 in which the fourth and fifth passages 30, 31 are omitted. Fig. 11 illustrates the second control mode in which the first passage 27 and the bypass 32 are open and the second and third passages 28, 29 are closed. This embodiment allows to apply the first control mode as illustrated in Figs. 7 and 10 and to apply the third control mode as illustrated in Figs. 5 and 8, as well. Fig. 11 shows that the bypass 32 is provided with a check valve 33, which allows oil flow from the first chamber 20 to the second chamber 20 only. The check valve 33 prevents the plunger 19 from rotating in the first rotational direction X in case the torque from at least one of the piston 12, the connecting rod 11 and the eccentric member 8 on the plunger 19 is temporarily directed in the first rotational direction X.
In the embodiment as shown in Fig. 11 the second hydraulic valve 26 and the hydraulic housing 24 are shaped such that the cross sectional area of the bypass 32 is variable upon moving the hydraulic valve 26 with respect to the hydraulic housing 24 such that oil flow rate through the bypass 32 can be controlled proportionally.
If in the embodiment of Fig. 11 the first hydraulic valve 25 is moved to the left the fourth and fifth passages 30, 31 are open and the first passage 27 is closed. This situation is comparable to the situation as shown in Fig. 9, which means that the plunger 19 will be moved in the second direction Y by means of the oil pump 35. The check valve 33 may remain closed such that the bypass 32 remains closed. If the second hydraulic valve 26 is moved to the right a situation which is comparable to the situation as shown in Fig. 10 is reached, i.e. the first passage 27 is closed, the second and third passages 28, 29 are open, the fourth and fifth passages 30, 31 are closed, whereas the bypass 32 remains closed. This means that the plunger 19 will be moved in the first rotational direction X by means of the oil pump 35.
Fig. 12 shows an alternative embodiment, which is comparable to the embodiment as shown in Fig. 11, but which has a further closable bypass 32', which is open when the second hydraulic valve 26 is moved to the right. The further bypass 32' is provided with a further check valve 33', which allows oil flow from the second chamber 21 to the first chamber 20 only. This provides the opportunity to move the plunger 19 in the first rotational direction X if the mechanical power source exerts a torque on the plunger 19 in the first rotational direction X.
In the embodiment as shown in Fig. 12 the second hydraulic valve 26 and the hydraulic housing 24 are shaped such that the cross sectional areas of the bypass 32 and of the further bypass 32' are variable such that respective oil flow rates through the bypass 32 and the further bypass 32' can be controlled proportionally to the relative position of the second hydraulic valve 26 in the hydraulic housing 24.
Fig. 12 also shows a pressure relief valve 34 which opens a channel between the first and second oil chambers 20, 21 if the pressure difference between the first and second oil chambers 20, 21 exceeds a certain level. This protects the gears 14-16 against damage due to a too high torque of the plunger 19 onto the control shaft 17. The pressure relief valve 34 may be arranged such that the engine 1 automatically switches to a lower compression ratio upon opening. Such a pressure relief valve may also be applied in the embodiments as described hereinbefore.
Figs. 13-15 show another alternative embodiment in which the fourth and fifth passages are omitted. Fig. 13 illustrates the third control mode, in which the first passage 27 is open, the second and third passages 28, 29 are closed and the bypass 32 is closed. Consequently, the plunger 19 remains at a fixed position within the actuator housing. Fig. 14 illustrates the first control mode, in which the first passage 27 is closed, the second and third passages 28, 29 are open and the bypass 32 is closed. This results in a movement of the plunger 19 in the first rotational direction X. Fig. 15 illustrates the second control mode, in which the mechanical power source exerts a torque on the plunger 19 in the second rotational direction Y, whereas the first passage 27 is open, the second and third passages 28, 29 are closed and the bypass 32 is open. In this case the mechanical power source moves the plunger 19 in the second rotational direction Y. The first, second and third passages 27, 28, 29 and the bypass 32 are opened and closed by simple respective hydraulic valves which are controlled by the control system CS.
The embodiments of the internal combustion engine 1 as described hereinbefore provide the opportunity to measure the oil pressure in at least one of the first and second oil chambers 20, 21, for example in the third control mode, on the basis of which the compression ratio is adjusted when the actual pressure at a certain engine operating point differs from a desired pressure at said engine operating point related to a desired compression ratio at that engine operating point by adjusting the position of the adjusting element towards a position where the difference decreases. This is a simple way to control the actual compression ratio.
The invention is not limited to the embodiments shown in the drawings and described hereinbefore, which may be varied in different manners within the scope of the claims and the technical equivalents. For example, the adjusting element may adjust an engine operating mode which is different from the compression ratio. Furthermore, the plunger may be movable linearly rather than in rotational direction. It is also noted that alternative control mechanisms for adjusting compression ratio are conceivable.
It is also possible to omit the second oil chamber, such that the second passage is used for moving the plunger in the first direction in the first control mode and to use the mechanical power source to move the plunger in the opposite direction in the second control mode. In the second control mode the first and second passages can be open to allow oil to flow away from the first oil chamber to the oil line. In the third control mode the first passage may be open and the second passage may be closed so as to keep the oil in the first oil chamber. Several alternative embodiments and control options are conceivable in combination with the feature that in the first control mode the first passage is closed such that the oil pump communicates with the first oil chamber only.

Claims

An internal combustion engine (1), comprising an oil pump (35), an oil line (22) being fluidly connected to the oil pump (35) and engine parts to be lubricated and a hydraulic actuator (18) including an actuator housing which accommodates a movable plunger (19) and an oil chamber (20), which plunger (19) is drivably coupled to an adjusting element (17) for adjusting an engine operating mode, wherein the engine (1) is provided with a control system (CS) including a first control mode for moving the plunger (19) in a first direction (X), a second control mode for moving the plunger (19) in a second direction (Y) which is opposite to the first direction (X) and a third control mode for maintaining the plunger (19) at a fixed position within the actuator housing, characterized in that the engine (1) is provided with a first passage (27) in the oil line (22) and a second passage (28) between the oil line (22) at an upstream side of the first passage (27) and the oil chamber (20), which first passage (27) is closable by the control system (CS), wherein the control system (CS) is configured such that under operating conditions in the first control mode the first passage (27) is closed such that the oil pump (35) communicates with the oil chamber (20) only.
An internal combustion engine (1), wherein the oil chamber is a first oil chamber (20) and the actuator housing accommodates a second oil chamber (21) wherein the first and second oil chambers (20, 21) are located at respective opposite sides of the plunger (19) and the second oil chamber (21) communicates with a third passage (29).
An internal combustion engine (1) according to claim 2, wherein the third passage (29) is provided between the oil line (22) at a downstream side of the first passage (27) and the second oil chamber (21) such that in the first control mode the third passage (29) allows oil to flow from the second oil chamber (21) to the engine parts to be lubricated.
An internal combustion engine (1) according to any one of the preceding claims, wherein the engine (1) comprises a mechanical power source (8, 11, 13) which is drivably coupled to the adjusting element (17) such that under operating conditions the adjusting element (17) transfers a force from the mechanical power source (8, 11, 13) to the plunger (19) in the second direction (Y).
An internal combustion engine (1) according to claim 4, wherein the second passage (28) is closable by the control system (CS) and the oil chamber (20) communicates with an oil drain line for discharging oil from the oil chamber (20) which oil drain line is closable by the control system (CS), wherein the control system (CS) is configured such that under operating conditions in the first control mode the second passage (28) is open and the oil drain line is closed and in the second control mode at least one of the second passage (28) and the oil drain passage is open.
An internal combustion engine (1) according to claim 5, wherein the oil drain line is incorporated in the closable second passage (28), wherein the control system (CS) is configured such that under operating conditions in the first control mode the second passage (28) is open and in the second control mode the first and second passages (28) are open.
An internal combustion engine (1) according to claim 4 and to claim 2 or 3, wherein the engine (1) is provided with a bypass (32) between the first and second oil chambers (20, 21), which bypass (32) is closable by the control system (CS), wherein the control system (CS) is configured such that under operating conditions in the first control mode the bypass (32) is closed and in the second control mode the bypass (32) is open, wherein the bypass (32) may be provided with a check valve (33) which allows oil flow from the first (20) to the second oil chamber (21) only.
An internal combustion engine (1) according to any one of the preceding claims, wherein the second passage (28) is closable by the control system (CS) and the control system (CS) is configured such that under operating conditions in the third control mode the first passage (27) is open and the second passage (28) is closed.
An internal combustion engine according to claim 3, wherein the engine is provided with a fourth passage (30) between the oil line (22) at an upstream side of the first passage (27) and the second oil chamber (21), and a fifth passage (31) between the oil line (22) at a downstream side of the first passage (27) and the first oil chamber (20), wherein the second, third, fourth and fifth passages (28, 29, 30, 31) are closable by the control system (CS), wherein the control system (CS) is configured such that under operating conditions in the second control mode the first, second and third passages (27, 28, 29) are closed and the fourth and fifth passages (30, 31) are open and in the first control mode the second and third passages (28, 29) are open and the fourth and the fifth passages (30, 31) are closed.
An internal combustion engine (1) according to claim 9, wherein the control system (CS) is configured such that under operating conditions in the third control mode the first passage (27) is open, whereas the second, third, fourth and fifth passages (28-31) are preferably closed.
An internal combustion engine (1) according to any one of the preceding claims and claim 4, wherein the engine has at least a crankcase (2), a piston (13), a connecting rod (11) that is rotatably mounted to the crankcase (2), a crankshaft (3) and a control mechanism (8, 14, 15, 16) for adjusting the compression ratio of the engine (1), to which control mechanism the adjusting element (17) is drivably coupled, wherein the mechanical power source is formed by at least one of the piston (13), the connecting rod (11) and the control mechanism (8, 14, 15, 16) exerting a force on the adjusting element (17) under operating conditions.
An internal combustion engine (1) according to claim 11, wherein the control mechanism comprises an eccentric member (8) which is rotatably mounted on a crankpin (6) of the crankshaft (3), the connecting rod (11) is rotatably mounted on the eccentric member (8) and the adjusting element comprises a control shaft (17) which extends through the crankshaft (3) and which is rotatable with respect to the crankshaft (3) about the crankshaft axis (4), wherein the eccentric member (8) is drivably coupled to the control shaft (17) through a transmission (14, 15, 16), which is adapted such that under operating conditions the eccentric member (8) rotates about the crankpin (6) at half speed of the crankshaft (3), when the control shaft (17) has a fixed rotational position with respect to the crankcase (2).
An internal combustion engine (1) according to any one of the preceding claims, wherein the plunger (19) is rotatable within the actuator housing.
A method of operating the internal combustion engine according to any one of the preceding claims and claim 11 or 12 and claim 2, wherein at least in one of the first and second oil chambers (20, 21), or the oil chamber (20), the actual pressure is measured, on the basis of which the compression ratio is adjusted when the actual pressure at a certain engine operating point differs from a desired pressure at said engine operating point by adjusting the position of the adjusting element (17) towards a position where the difference decreases.
A method according to claim 13, wherein the engine operating point is defined by engine speed and load.