An internal combustion engine including variable compression ratio and a method of operating the engine

Abstract

 An internal combustion engine (1) including variable compression ratio comprises a crankcase, a crankshaft (3) including a crankshaft axis (4), wherein the crankshaft (3) has at least a central main portion (5), a crankpin (6) and a crankshaft web (7) located between the central main portion (5) and the crankpin (6). The crankshaft (3) is supported by the crankcase and rotatable with respect thereto about the crankshaft axis (4). The engine comprises at least a connecting rod including a big end and a small end, a piston being rotatably connected to the small end, and a crank member (8) which is rotatably mounted on the crankpin (6), and comprises at least a bearing portion which is eccentrically disposed with respect to the crankpin (6), and has an outer circumferential wall which bears the big end of the connecting rod such that the connecting rod is rotatably mounted on the bearing portion of the crank member (8) via the big end. The engine also comprises a driving mechanism (2) for rotating the crank member (8) with respect to the crankshaft (3), which comprises a drive shaft (9) that extends concentrically through the central main portion (5). The drive shaft (9) is drivably coupled to the crank member (8) via a transmission (10) at a side of the crankshaft web (7) where the crankpin (6) is located. At the opposite side of the crankshaft web (7) the drive shaft (9) is drivably coupled to the crankshaft (3) via an external satellite gear (13) that is rotatably mounted to the crankshaft (3) and rotatable with respect to the crankshaft (3) about a satellite axis extending parallel to the crankshaft axis (4). The satellite gear (13) meshes with an internal ring gear (14) having a centre line that coincides with the crankshaft axis (4) and with an external sun gear (15) that is fixed to the drive shaft (9). The driving mechanism (2) is adapted such that under operating conditions the crank member (8) rotates at a rotation frequency with respect to the crankcase which is half of that of the crankshaft (3).

Description

[0001] The present invention pertains to an internal combustion engine including variable compression ratio.

[0002] An engine with variable compression ratio is well-known in the field of spark-ignition engines. It provides the opportunity to operate the engine at high efficiency, particularly under part-load conditions. Increasing the compression ratio leads to decreasing fuel consumption. At high-load or full-load the compression ratio must be lowered in order to avoid knocking. Several earlier applications of the applicant disclose internal combustion engines with variable compression ratio, for example WO 2009/018863.

[0003] An object of the invention is to provide an improved engine.

[0004] This is achieved by the internal combustion engine according to claim 1.

[0005] The planetary concept of the ring gear, the sun gear and the satellite gear provides a compact driving mechanism.

[0006] In a practical embodiment the transmission comprises an external crank member gear which is fixed to the crank member and an external drive shaft gear which is fixed to the drive shaft and meshes with the crank member gear, wherein the drive shaft gear and the crank member gear are dimensioned such that under operating conditions the crank member rotates in the same rotational direction as the crankshaft as seen from the crankcase. This means that friction between the crank member and the crankpin is relatively low.

[0007] It is noted that more than one satellite gear may be present to evenly distribute force.

[0008] The satellite gear may be rotatably mounted to a circular support member that is fixed to the central main portion of the crankshaft.

[0009] The support member may be fixed by a nut through which the drive shaft extends.

[0010] The support member may be provided with a driving wheel for driving auxiliary devices of the engine. The integration of the driving wheel and the satellite gear on the support member is advantageous in terms of compactness.

[0011] The ring gear may be turnable with respect to the crankcase so as to adjust the rotational position of the crank member at a virtual standstill of the crankshaft. The ring gear can be turned over a certain angle in one direction to reduce compression ratio and in opposite direction to increase compression ratio.

[0012] The invention is also related to a method of operating the internal combustion engine as described hereinbefore, wherein the ring gear is unlocked with respect to the crankcase and the ring gear is rotated with respect to the crankcase by means of combustion forces of the engine so as to change its compression ratio. During the time period of decoupling the ring gear the combustion forces will force the ring gear to a different rotational position with respect to the crankcase. The engine may comprise a coupling element for coupling and decoupling which may be electronically controlled, for example.

[0013] Alternatively, the ring gear is unlocked with respect to the crankcase and the drive shaft is accelerated or decelerated so as to change the rotational position of the ring gear with respect to the crankcase and thus the compression ratio of the engine. In case of the presence of a pulley on the drive shaft for driving an alternator, the drive shaft can be decelerated by means of braking with the alternator; similarly, it can be accelerated when the alternator has an electric motor function.

[0014] The invention will hereafter be elucidated with reference to the schematic drawings showing an embodiment 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, but without the crankshaft and the pulley.

Fig. 3 is a perspective view of a part of the embodiment as shown in Fig. 1 on a larger scale.

[0015] Figs. 1 and 2 show a part of an embodiment of an internal combustion engine 1 according to the invention. The engine 1 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 embodiment of the engine 1 as shown in Figs. 1 and 2 is provided with a driving mechanism 2 which is used for varying the compression ratio and which is located at a front side of the engine 1. An opposite rear side of the engine 1 is provided with a flywheel (not shown). In Figs. 1 and 2 the front side of the engine is located at the left side in the drawings.

[0016] The internal combustion engine 1 comprises a crankcase (not shown) which supports a crankshaft 3 via bearings. The crankshaft 3 is rotatable with respect to the crankcase about a crankshaft axis 4. At the front side of the engine 1 where the driving mechanism 2 is located, the crankshaft 3 has a central main portion 5, a crankpin 6 and a crankshaft web 7. The crankshaft web 7 is located between the central main portion 5 and the crankpin 6 as seen along the crankshaft axis 4.

[0017] The embodiment of the engine 1 as shown in Figs. 1 and 2 is a four-cylinder engine and has four crankpins 6 and four pairs of crankshaft webs 7 each at opposite ends of each crankpin 6, whereas similar central main portions 5 are located between crankshaft webs 7 at sides thereof opposite to the sides where the respective crankpins 6 are located. The driving mechanism 2 is also applicable for engines having a different number of cylinders. For explanatory reasons herein the central main portion 5, crankpin 6 and crankshaft web 7 closest to the front side of the engine 1 are referred to as the central main portion 5, the crankpin 6 and the crankshaft web 7, respectively. The engine 1 is also provided with connecting rods, each including a big end and a small end, and pistons which are rotatably connected to the respective small ends. These parts are not shown for clarity reasons.

[0018] The engine 1 comprises a crank member 8 which is rotatably mounted on the crankpin 6. The crank member 8 comprises a bearing portion which is eccentrically disposed with respect to the crankpin 6. The bearing portion has an outer circumferential wall which bears the big end of the corresponding connecting rod such that the connecting rod is rotatably mounted on the bearing portion of the crank member 8 via the big end. In the embodiment as shown in Figs. 1 and 2 the bearing portion of the crank member 8 is located between two external gears.

[0019] The driving mechanism 2 is configured such that under operating conditions the crank member 8 is rotated at a rotation frequency with respect to the crankcase which is half of that of the crankshaft 3 and in the same rotational direction as that of the crankshaft 3 as seen from the crankcase. Hence, a single revolution of the crank member 8 with respect to the crankcase corresponds to two revolutions of the crankshaft 3 with respect to the crankcase.

[0020] The driving mechanism 2 comprises a drive shaft 9, see Fig. 2, which extends concentrically through the central main portion 5 of the crankshaft 4. The drive shaft 9 is mechanically coupled to the crank member 8 via a transmission 10 located at a side of the crankshaft web 7 where the crankpin 6 is located. In this case the transmission 10 comprises an external crank member gear 11 of the crank member 8 and an external drive shaft gear 12 which is fixed to the drive shaft 9. The drive shaft gear 12 meshes with the crank member gear 11.

[0021] In case of an engine 1 having a plurality of cylinders including a plurality of crank members 8, such as in the embodiment as shown in Figs. 1 and 2, the crank members 8 are mechanically coupled to each other such that all crank members 8 are rotated in a similar manner with respect to the crankcase. In this case the crank members 8 are coupled to each other through external gears which mesh with external gears of the respective crank members 8 and which are fixed to common shafts extending concentrically through the respective central main portions 5 and corresponding crankshaft webs 7 at both sides of the respective central main portions 5 of the crankshaft 3. This is illustrated in Fig. 2.

[0022] The drive shaft 9 extends concentrically through the central main portion 5 at a side of the crankshaft web 7 opposite to the side where the crankpin 6 is located and is drivably coupled to the crankshaft 3. Figs. 1 and 2 show that in this case the driving mechanism 2 comprises a planetary gear system through which the crankshaft 3 drives the drive shaft 9. The planetary gear system comprises three external satellite gears 13, an internal ring gear 14 including a centre line that coincides with the crankshaft axis 4 and an external sun gear 15 that is fixed to a portion of the drive shaft 9 that projects from the central main portion 5 at the front side of the engine 1. The mentioned portion of the drive shaft 9 lies in a common plane with the ring gear 14 and the satellite gear 13.

[0023] Each of the satellite gears 13 is rotatably mounted to a circular support member 16, which is shown as a separate part in Fig. 3. The support member 16 is fixed to the central main portion 5 of the crankshaft 3. The satellite gears 13 are rotatable about respective satellite gear axes extending parallel to the crankshaft axis 4. Each of the satellite gears 13 meshes with the ring gear 14, on the one hand, and with the sun gear 15, on the other hand. The support member 16 is also provided with a driving wheel in the form of a toothed ring wheel 17 for driving other auxiliary devices of the engine 1, for example an oil pump, a camshaft, or the like.

[0024] The dimensions of the planetary gear system, the crank member gear 11 and the drive shaft gear 12 are selected such that the crank member 8 rotates at half crankshaft speed with respect to the crankcase. In the embodiment as shown the diameters of the crank member gear 11 and the drive shaft gear 12 are 75 and 22.5 mm, respectively, hence a gear ratio of 0.3. The diameters of the satellite gears 13, the ring gear 14 and the sun gear 15 are 21, 105 and 63 mm, respectively. Alternative dimensions are conceivable.

[0025] The support member 16 is fixed to the crankshaft 3 by a nut 18 through which the drive shaft 9 extends. Since the rotational position of the support member 16 upon fixing it to the crankshaft 3 is not relevant the nut 18 may be integral with the support member 16. The nut 18 may be partly or entirely located within the circumferential wall of the support member 16, which is advantageous in terms of compactness in longitudinal direction of the engine 1.

[0026] Looking to the front side of the engine 1 and assuming that the crankshaft 3 rotates clockwise in case the ring gear 14 has a fixed position with respect to the crankcase, the satellite gears 13 rotate anti-clockwise about their respective satellite gear axes at 105/21 times crankshaft speed, whereas the satellite gear axes rotate clockwise at crankshaft speed. Consequently, the sun gear 15 rotates clockwise with respect to the crankcase at 21/63 x 105/21 times crankshaft speed, which means that the drive shaft 9, and also the drive shaft gear 12, rotates clockwise at about 1,67 times crankshaft speed. Due to the gear ratio of the transmission 10 the crank member 8 rotates at 0.3 x 1,67 = 0,5 times crankshaft speed with respect to the crankpin 6 and anti-clockwise. If the crank member 8 was fixed to the crankshaft 3 the crank member 8 would also be rotated clockwise at crankshaft speed with respect to the crankcase; however, after one revolution of the crankshaft 3 it is now rotated a half revolution anti-clockwise with respect to the crankpin 6. This implies that after one revolution of the crankshaft 3 the crank member 8 is also rotated clockwise, but a half revolution, with respect to the crankcase.

[0027] The relationship between the gears can be expressed by the following formulas:

wherein
n_ds = speed of drive shaft with respect to crankcase
n_cs = speed of crankshaft with respect to crankcase
N_cmg = number of teeth of crank member gear
N_ds = number of teeth of drive shaft gear.

wherein
N_ds2 = number of teeth of sun gear
N_rg = number of teeth of ring gear

[0028] Hence,

[0029] Figs. 1 and 2 also illustrate that the crank member gear 11 has a larger diameter than the external gear at the opposite side of the bearing portion. The latter gear has the same diameter as the external gears of the other crank members of the engine 1 which do not directly engage the driving mechanism 2. The reason of the relatively large diameter of the crank member gear 11 is that in the embodiment as shown in the figures the diameter of the satellite gears would become too small if the diameter of the crank member gear was selected smaller.

[0030] In order to change the compression ratio of the engine 1 the rotational position of the ring gear 14 with respect to the crankcase is adjustable by means of an actuator, for example hydraulically (not shown). Due to turning the ring gear 14 the rotational position of the crank member 8 is turned about the crankpin 6 at a virtual standstill of the crankshaft 3.

[0031] Fig. 1 shows that a pulley 19 is fixed to the drive shaft 9. The pulley 19 may be drivably coupled to auxiliary devices of the engine 1, for example an alternator.

[0032] It is noted that the rotational position of the ring gear 14 with respect to the crankcase can be adjusted by means of combustion forces and/or accelerating and/or decelerating the pulley 19 during a period of unlocking the ring gear 14 with respect to the crankcase. For example, an electronically or hydraulically controlled locking element may be present between the ring gear 14 and the crankcase for the action of unlocking.

[0033] A manner of adjusting compression ratio by utilizing combustion forces can be explained for the embodiment as shown in Figs. 1 and 2 as follows. Under practical conditions the rotational position of the crank member 8 with respect to the crankpin 6 may be such that at maximum compression ratio at the end of the compression stroke, when the piston is in top dead centre, a centre line of the bearing portion lies beyond a centre line of the crank pin 6 as seen from the crankshaft axis 4, whereas the centre line of the bearing portion, the centre line of the crankpin 6 and the crankshaft axis 4 lie in a common plane. The compression ratio can be reduced by turning the crank member 8 from this position about its centre line relative to the crankpin 6 in its rotational direction with respect to the crankcase under normal operating conditions at a virtual standstill of the crankshaft 3 over a certain turning angle. It is assumed in this case that the rotational direction with respect to the crankcase under normal operating conditions is clockwise, and in the same direction as the crankshaft 3, when looking to the front side of the engine 1. The minimum compression ratio at the end of the compression stroke, when the piston is in top dead centre, may lie at a turning angle of the crank member of 90° to 140 ° from the above-mentioned position at maximum compression ratio with respect to the crankcase, for example.

[0034] Due to the presence of the eccentricity of the crank member 8, and in this case a plurality of crank members, the combustion forces of the pistons exert a continuous average torque onto the drive shaft gear 12 via the crank member gears. Due to the selected rotational directions of the crankshaft 3 and the crank member 11 there is a continuous average torque on the ring gear 14 in clockwise direction. This means that upon decoupling the ring gear 14 with respect to the crankcase there is a natural force for accelerating the ring gear 14 in clockwise direction. Accelerating the ring gear 14 clockwise implies rotating the crank member 8 clockwise at virtual standstill of the crankshaft 3, i.e. in a direction of reduced compression ratio.

[0035] Similarly, in case the pulley is decelerated clockwise during a period of unlocking the ring gear 14 with respect to the crankcase, for example by means of braking it via an alternator that is driven by the pulley 19, the ring gear 14 is turned clockwise at virtual standstill of the crankshaft 3, resulting in reduced compression ratio.

[0036] In case the pulley 19 is accelerated clockwise during a period of unlocking the ring gear 14 with respect to the crankcase, for example by means of an electric motor, the ring gear 14 is turned anti-clockwise, resulting in increased compression ratio.

[0037] In order to monitor the compression ratio the rotational position of the ring gear 14 can be measured by means of a potmeter, for example. It is possible to apply a transmission between the potmeter and the ring gear 14, but it is also conceivable to use the ring gear 14 itself as a rotational part of a potmeter.

[0038] From the foregoing, it will be clear that the invention provides a compact driving mechanism for rotating the crank member.

[0039] The invention is not limited to the embodiment shown in the drawings and described hereinbefore, which may be varied in different manners within the scope of the claims and their technical equivalents. For example, the transmission may be configured such that the crank member is rotated in opposite direction of the crankshaft as seen from the crankcase.

Claims

1. An internal combustion engine (1) including variable compression ratio, comprising
a crankcase,
a crankshaft (3) including a crankshaft axis (4), said crankshaft (3) having at least a central main portion (5), a crankpin (6) and a crankshaft web (7) located between the central main portion (5) and the crankpin (6), said crankshaft (3) being supported by the crankcase and rotatable with respect thereto about the crankshaft axis (4),
at least a connecting rod including a big end and a small end,
a piston being rotatably connected to the small end,
a crank member (8) being rotatably mounted on the crankpin (6), and comprising at least a bearing portion which is eccentrically disposed with respect to the crankpin (6), and having an outer circumferential wall which bears the big end of the connecting rod such that the connecting rod is rotatably mounted on the bearing portion of the crank member (8) via the big end,
a driving mechanism (2) for rotating the crank member (8) with respect to the crankshaft (3), which comprises a drive shaft (9) that extends concentrically through the central main portion (5), wherein the drive shaft (9) is drivably coupled to the crank member (8) via a transmission (10) at a side of the crankshaft web (7) where the crankpin (6) is located, wherein the drive shaft (9) at the opposite side of the crankshaft web (7) is drivably coupled to the crankshaft (3) via an external satellite gear (13) that is rotatably mounted to the crankshaft (3) and rotatable with respect to the crankshaft (3) about a satellite axis extending parallel to the crankshaft axis (4), wherein the satellite gear (13) meshes with an internal ring gear (14) having a centre line that coincides with the crankshaft axis (4) and with an external sun gear (15) that is fixed to the drive shaft (9), wherein the driving mechanism (2) is adapted such that under operating conditions the crank member (8) rotates at a rotation frequency with respect to the crankcase which is half of that of the crankshaft (3).

2. An internal combustion engine (1) according to claim 1, wherein the transmission (10) comprises an external crank member gear (11) which is fixed to the crank member (8) and an external drive shaft gear (12) which is fixed to the drive shaft (9) and meshes with the crank member gear (11), wherein the drive shaft gear (12) and the crank member gear (11) are dimensioned such that under operating conditions the crank member (8) rotates in the same rotational direction as the crankshaft (3) as seen from the crankcase.

3. An internal combustion engine (1) according to claim 1 or 2, wherein the satellite gear (13) is rotatably mounted to a circular support member (16) that is fixed to the central main portion (5) of the crankshaft (3).

4. An internal combustion engine (1) according to claim 3, wherein the support member (16) is fixed by a nut (18) through which the drive shaft (9) extends.

5. An internal combustion engine (1) according to claim 3 or 4, wherein the support member (16) is provided with a driving wheel (17) for driving auxiliary devices of the engine (1).

6. An internal combustion engine (1) according to one of the preceding claims, wherein the ring gear (14) is rotatable with respect to the crankcase so as to adjust the rotational position of the crank member (8) at a virtual standstill of the crankshaft (3).

7. A method of operating the internal combustion engine (1) according to claim 6, wherein the ring gear (14) is unlocked with respect to the crankcase and the ring gear (14) is rotated with respect to the crankcase by means of combustion forces of the engine (1) so as to change its compression ratio.

8. A method of operating the internal combustion engine (1) according to claim 6, wherein the ring gear (14) is unlocked with respect to the crankcase and the drive shaft (9) is accelerated or decelerated so as to change the compression ratio of the engine (1).

Drawing