AN INTERNAL COMBUSTION ENGINE

Abstract

 An internal combustion engine (1) comprises a crankshaft (3) having at least a crankpin (4), an eccentric element (6) for supporting a connecting rod (9), which is rotated on the crankpin (4) by an adjusting shaft (15) to vary its compression ratio, which adjusting shaft (15) extends concentrically through the crankshaft (2), an internal transmission (12, 13, 14) through which the eccentric element (6) is coupled to the adjusting shaft (15), wherein the internal transmission (12, 13, 14) is adapted such that when the adjusting shaft (15) has a fixed angular position with respect to the engine block (2) under operating conditions the eccentric element (6) rotates with respect to the crankpin (4) in opposite direction of the direction in which the crankshaft (3) rotates with respect to the engine block (2) about the crankshaft axis (5) and at half speed thereof, a drive shaft (17) for driving the adjusting shaft (15) through an external transmission (18, 19) which engages the adjusting shaft (15) at a distance from a location where the internal transmission (12, 13, 14) engages the adjusting shaft (15), wherein the drive shaft (17) is rotatably mounted to the engine block (2), a drive unit (20, 28) for driving the drive shaft (17), wherein the drive shaft (17) extends parallel to the adjusting shaft (15) outside the crankshaft (3) and the drive unit (20, 28) engages the drive shaft (17) at a distance from a location where the external transmission (18, 19) engages the drive shaft (17).

Description

[0001] The present invention relates to an internal combustion engine, comprising an engine block, a crankshaft having at least a crankpin, the crankshaft being supported by the engine block and rotatable with respect thereto about a crankshaft axis, an eccentric element for supporting a connecting rod, which eccentric element is rotatably mounted on the crankpin, an adjusting shaft for varying the rotational position of the eccentric element with respect to the crankshaft at a virtual standstill of the engine so as to vary its compression ratio, which adjusting shaft extends concentrically through the crankshaft such that its centreline coincides with the crankshaft axis and which adjusting shaft is rotatable with respect to the crankshaft, an internal transmission through which the eccentric element is drivably coupled to the adjusting shaft, wherein the internal transmission is adapted such that when the adjusting shaft has a fixed angular position with respect to the engine block under operating conditions the eccentric element rotates with respect to the crankpin in opposite direction of the direction in which the crankshaft rotates with respect to the engine block about the crankshaft axis and at half speed thereof, a drive shaft for driving the adjusting shaft through an external transmission which external transmission engages the adjusting shaft at a distance from a location where the internal transmission engages the adjusting shaft, and wherein the drive shaft is rotatably mounted to the engine block, and a drive unit for driving the drive shaft.

[0002] Such an engine is known from WO 2013/110700. Under operating conditions the crankshaft rotates at a certain speed. When it is desired to adjust the compression ratio of the engine the adjusting shaft can be turned with respect to the engine block to a different angular position, i.e. with respect to the crankshaft at a virtual standstill thereof. The external transmission of the known engine comprises a worm gear transmission between the drive shaft and the adjusting shaft.

[0003] An object of the invention is to provide a compact internal combustion engine.

[0004] This object is accomplished with the internal combustion engine according to the invention, wherein the drive shaft extends parallel to the adjusting shaft outside the crankshaft and the drive unit engages the drive shaft at a distance from a location where the external transmission engages the drive shaft as seen in a direction from the external transmission to the internal transmission.

[0005] An advantage of the location where the drive unit engages the drive shaft and the orientation of the drive shaft is that the engine can have a compact design whereas parts that are vulnerable to damage caused by impact from outside, such as a drive unit or a part thereof, are located remote from a front side of the engine where the external transmission is located. For example, when the engine is applied in a motorcycle in which the crankshaft extends transversely with respect to the direction of driving the external transmission may be located at one of the lateral sides of the motorcycle, since the front side of the engine is located at one of the lateral sides of the motorcycle. When the drive unit is located at a distance from the lateral sides of the motorcycle the risk of damage caused by external impact thereon is minimized.

[0006] It is noted that the crankpin is located eccentrically with respect to a main portion of the crankshaft which main portion has a centreline that coincides with the crankshaft axis. The crankpin and the main portion are connected to each other through a crank arm. The internal transmission is located at a side of the crank arm where the crankpin is located and the external transmission is located at the opposite side of the crank arm. In practice, the adjusting shaft may project from an axial end of the crankshaft at the side of the crank arm opposite to the side where the crankpin is located. The external transmission may engage the adjusting shaft at the projecting portion.

[0007] The external transmission may comprise a first external gear which is fixed to the drive shaft and a second external gear which is fixed to the adjusting shaft, wherein the first and second external gears mesh with each other.

[0008] The diameter of the second external gear may be larger than the diameter of the first external gear. For example, it may be more than twice as large as the diameter of the first external gear. This provides the opportunity to create a relatively large distance between the adjusting shaft and the drive shaft and provides the opportunity to turn the adjusting shaft by applying a relatively low torque on the drive shaft.

[0009] In a practical embodiment the drive unit comprises an electric motor.

[0010] The electric motor may be mounted at an outer side of the engine block. The drive shaft may be located at an outer side of the engine block, as well, but it may also be located inside the engine block or partly inside the engine block.

[0011] The electric motor may have an output shaft which is drivably coupled to the drive shaft, whereas the output shaft and the drive shaft are angled with respect to each other. Several coupling mechanisms for coupling the output shaft and the drive shaft to each other are conceivable, for example a worm gear transmission.

[0012] In a particular embodiment the engine is provided with a starter motor for starting the engine, wherein the electric motor and the starter motor form an integral drive motor for driving either the crankshaft upon starting the engine or the drive shaft after the engine has been started, wherein an output shaft of the integral drive motor is coupled to the crankshaft through a freewheel mechanism, on the one hand, and to the drive shaft through a controllable clutch, on the other hand. Upon starting the engine the clutch can be switched such that the output shaft of the integral drive motor is decoupled from the drive shaft. In this situation the integral drive motor can be driven at a relatively high speed for starting the engine. After the engine has been started the freewheel mechanism automatically decouples the crankshaft from the integral drive motor. When the engine is running the clutch can be switched such that it couples the integral drive motor to the drive shaft such that the integral drive motor can be operated for turning the adjusting shaft. In this condition the integral drive motor is operated at a much lower speed than in case of driving the crankshaft upon starting the engine. Besides, the integral drive motor may be operated in opposite directions for adjusting the compression ratio.

[0013] In a preferred embodiment the engine is provided with a spring between the engine block and at least one of the first and second external gears, which spring exerts a force between the engine block and the at least one of the first and second external gears in longitudinal direction of the drive shaft and the adjusting shaft, respectively. The spring creates a friction force between the at least one of the first and second external gears, on the one hand, and the engine block, on the other hand, such that a minimum force level must be exceeded to turn the corresponding external gear. This reduces the risk of vibration between the external gears and thus reduces the risk of noise generation under operating conditions, which vibration may be generated by reciprocating forces on the adjusting shaft via the connecting rod due to combustion forces and inertia forces on the connecting rod. Consequently, the external gears do not require tight tolerances.

[0014] The spring may have a ring shape and extend about one of the first and second external gears. It may be a wave spring, for example.

[0015] The invention will hereafter be elucidated with reference to very 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 perspective view of a part of the embodiment of Fig. 1 on a larger scale and seen from a different side.

Fig. 3 is a similar view as Fig. 1, but seen from a different side.

Fig. 4 is a perspective sectional view of the part as shown in Fig. 3.

Fig. 5 is a similar view as Fig. 4, but in which parts are not shown for explanatory reasons.

Fig. 6 is a similar view as Fig. 4, but showing a different section.

Fig. 7 is an illustrative view of the embodiment as shown in Figs. 1-6.

Fig. 8 is a similar view as Fig. 7, but showing an alternative embodiment.

[0016] Fig. 1-7 show a part of an embodiment of an internal combustion engine 1 according to the invention. The engine 1 is a single-cylinder engine which is typically applied in motorcycles, but alternative applications are conceivable. The engine 1 comprises an engine block 2, which supports a crankshaft 3 by crankshaft bearings 2a, see Fig. 6. The crankshaft 3 includes a crankpin 4 and is rotatable with respect to the engine block 2 about a crankshaft axis 5.

[0017] The engine 1 comprises an eccentric element 6 which is rotatably mounted on the crankpin 4. The eccentric element 6 is provided with a bearing portion 7 which is disposed eccentrically with respect to the crankpin 4, see Fig. 2. The bearing portion 7 has an outer circumferential wall which bears a big end 8 of a connecting rod 9. The connecting rod 9 also includes a small end 10 to which a piston 11 is rotatably connected. The crankshaft 3 and connecting rod 9 are not shown in Fig. 2 for explanatory reasons.

[0018] The eccentric element 6 is provided with an eccentric element gear 12 which meshes with a first intermediate gear 13a. The first intermediate gears 13a is rotatably mounted to the crankshaft 3 and its axis of rotation extends parallel to the crankshaft axis 5. The first intermediate gear 13a is fixed to a second intermediate gear 13b and their axis of rotation coincide. The diameter of the second intermediate gear 13b is smaller than the diameter of the first intermediate gear 13a. The second intermediate gear 13b meshes with an auxiliary gear 14. The auxiliary gear 14 is fixed to an adjusting shaft 15. The adjusting shaft 15 extends concentrically through the crankshaft 3 and is supported by the crankshaft 3. The adjusting shaft 15 is rotatable with respect to the crankshaft 3 about the crankshaft axis 5. Thus, the adjusting shaft 15 is rotatable about an adjusting shaft axis which coincides with the crankshaft axis 5. As a consequence, the centre line of the auxiliary gear 14 coincides with the crankshaft axis 5. The eccentric element gear 12, the first and second intermediate gears 13a, 13b and the auxiliary gear 14 form an internal transmission through which the eccentric element 6 and the adjusting shaft 15 are drivably coupled to each other.

[0019] Figs. 1 and 6 show that the auxiliary gear 14, the first and second intermediate gears 13a, 13b and the eccentric element gear 12 are mounted at the same side of a crank arm 16 of the crankshaft 3. The crank arm 16 and a main portion of the crankshaft at the crankshaft bearing 2a are integrated such that the adjusting shaft 15 extends through both. Thus, the adjusting shaft 15 extends within the main portion of the crankshaft.

[0020] The gear dimensions of the auxiliary gear 14, the first and second intermediate gears 13a, 13b and the eccentric element gear 12 are selected such that under operating conditions the eccentric element 6 rotates with respect to the crankpin 4 in opposite direction of the direction in which the crankshaft 3 rotates with respect to the engine block 2 about the crankshaft axis 5 and at half speed thereof when the adjusting shaft 15 is held at a fixed angular position with respect to the engine block 2.

[0021] The engine 1 as shown in Figs. 1-7 provides the opportunity to adjust the top dead centre of the piston 11, hence its compression ratio, by changing the angular position of the adjusting shaft 15 with respect to the engine block 2. Hence, the rotational position of the eccentric element 6 with respect to the crankshaft 3 can be varied at a virtual standstill of the crankshaft 3 so as to vary the compression ratio. The functioning of the engine is explained in more detail in WO 2013/110700.

[0022] Figs. 3-6 show a front side of the engine 1 in more detail. The figures show a drive shaft 17 for driving the adjusting shaft 15 through an external transmission. The external transmission comprises a first external gear 18 which is fixed to the drive shaft 17 and a second external gear 19 which is fixed to the adjusting shaft 15. The first and second external gears 18, 19 mesh with each other. The second external gear 19 is fixed to the adjusting shaft 15 at a distance from the auxiliary gear 14, at the opposite side of the crank arm 16 and at a portion of the adjusting shaft 15 which projects from the crankshaft 3 at the front side of the engine 1.

[0023] The drive shaft 17 extends parallel to the adjusting shaft 15 outside the crankshaft 3. In this case the drive shaft 17 also extends partly outside the engine block 2 as shown in Figs. 3 and 4. The diameter of the second external gear 19 is more than twice as large as the diameter of the first external gear 18. This provides the opportunity to locate the drive shaft 17 at a significant distance from the adjusting shaft 15, whereas torque level of the drive shaft 17 for turning the adjusting shaft 15 may be relatively low.

[0024] The engine 1 is provided with a drive unit in the form of an electric motor 20 for driving the drive shaft 17. The electric motor 20 is mounted to the engine block 2 at an outer side thereof and has an output shaft which is coupled to the drive shaft 17 through a worm gear transmission 31. This can be seen in Fig. 5, in which the engine block 2 is not shown for explanatory reasons. Due to the worm gear transmission 31 the output shaft of the electric motor 20 and the drive shaft 17 are angled with respect to each other. The output shaft of the electric motor 20 engages the drive shaft 17 at a distance from the first external gear 18, i.e. at a distance from a location where the external transmission engages the drive shaft 17 as seen in a direction from the external transmission to the internal transmission.

[0025] Figs. 3-7 show an alternator rotor 21 which is attached to the crankshaft 3 and which cooperates with an alternator stator 22 which is fixed to the engine block 2 through a yoke 23. The alternator rotor 21 and stator 22 form part of an electrical generator of the engine 1. The second gear 19 has an axially protruding receiving portion 24 at its centre for receiving the adjusting shaft 15 which is fixed within the protruding receiving portion 24. The protruding receiving portion 24 extends through a through-hole 25 in the yoke 23.

[0026] A ring-shaped wave spring 26 is mounted to the second gear 19 and biased by a cover 27 which is fixed to the yoke 23. This means that the wave spring 26 is sandwiched between the cover 27 and the second gear 19 and exerts a force between the engine block 2 and the second gear 19 in axial direction of the adjusting shaft 15. An advantage of this arrangement is that a permanent friction force exists between the second gear 19 and the engine block 2, which prevents the second gear 19 from easily vibrating about the crankshaft axis 5 against the first gear 18 and thus generating noise. Vibration of the second gear 19 may be generated by reciprocating forces of the connecting rod 9 on the adjusting shaft 15 as a result of combustion forces and inertia forces under operating conditions. It may be clear that the friction force between the second gear 19 and the engine block 2 should be low enough to enable the electric motor 20 to turn the adjusting shaft 15.

[0027] Fig. 7 is an illustrative view of the embodiment of the engine 1 as shown in Figs. 1-6. Fig. 7 shows a starter motor 28 which is coupled to the crankshaft 3 via a starter gear 29 and a freewheel mechanism 30 which is well-known to the skilled person. The freewheel mechanism 30 decouples the crankshaft 3 from the starter motor 28 as soon as the engine 1 runs. The electric motor 20 drives the drive shaft 17 through the worm gear transmission 31.

[0028] Fig. 8 is an illustrative view of an alternative embodiment of the engine 1. In this embodiment the starter motor 28 and the electric motor 20 are integrated and form an integral drive motor for driving either the crankshaft 3 upon starting the engine 1 or the drive shaft 17 through a clutch 32 after the engine 1 has been started. Upon starting the engine 1 the clutch 32 decouples the integral drive motor 20, 28 from the drive shaft 17. After the engine 1 has been started the freewheel mechanism 30 automatically decouples the crankshaft 3 from the integral drive motor 20, 28, whereas the clutch 32 couples the integral drive motor 20, 28 to the drive shaft 17 such that the integral drive motor 20, 28 can be operated for turning the adjusting shaft 15 via the external transmission 18, 19. Because of the friction between the second gear 19 and the engine block 2, due to the presence of the wave spring 26, the adjusting shaft 15 is maintained in its position during the period of starting the engine, i.e. during the period in which the integral drive motor 20, 28 and the drive shaft 17 are decoupled from each other through the clutch 32.

[0029] 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 their technical equivalents.

Claims

1. An internal combustion engine (1), comprising
an engine block (2),
a crankshaft (3) having at least a crankpin (4), said crankshaft (3) being supported by the engine block (2) and rotatable with respect thereto about a crankshaft axis (5),
an eccentric element (6) for supporting a connecting rod (9), which eccentric element (6) is rotatably mounted on the crankpin (4),
an adjusting shaft (15) for varying the rotational position of the eccentric element (6) with respect to the crankshaft (3) at a virtual standstill of the engine (1) so as to vary its compression ratio, which adjusting shaft (15) extends concentrically through the crankshaft (2) such that its centreline coincides with the crankshaft axis (5) and which adjusting shaft (15) is rotatable with respect to the crankshaft (3),
an internal transmission (12, 13, 14) through which the eccentric element (6) is drivably coupled to the adjusting shaft (15), wherein the internal transmission (12, 13, 14) is adapted such that when the adjusting shaft (15) has a fixed angular position with respect to the engine block (2) under operating conditions the eccentric element (6) rotates with respect to the crankpin (4) in opposite direction of the direction in which the crankshaft (3) rotates with respect to the engine block (2) about the crankshaft axis (5) and at half speed thereof,
a drive shaft (17) for driving the adjusting shaft (15) through an external transmission (18, 19) which external transmission (18, 19) engages the adjusting shaft (15) at a distance from a location where the internal transmission (12, 13, 14) engages the adjusting shaft (15), wherein the drive shaft (17) is rotatably mounted to the engine block (2),
a drive unit (20, 28) for driving the drive shaft (17),
wherein the drive shaft (17) extends parallel to the adjusting shaft (15) outside the crankshaft (3) and the drive unit (20, 28) engages the drive shaft (17) at a distance from a location where the external transmission (18, 19) engages the drive shaft (17) as seen in a direction from the external transmission (18, 19) to the internal transmission (12, 13, 14).

2. An internal combustion engine (1) according to claim 1, wherein the external transmission (18, 19) comprises a first external gear (18) which is fixed to the drive shaft (17) and a second external gear (19) which is fixed to the adjusting shaft (15), wherein the first and second external gears (18, 19) mesh with each other.

3. An internal combustion engine (1) according to claim 2, wherein the diameter of the second external gear (19) is larger than the diameter of the first external gear (18).

4. An internal combustion engine (1) according to any one of the preceding claims, wherein the drive unit comprises an electric motor (20, 28).

5. An internal combustion engine (1) according to claim 4, wherein the electric motor (20, 28) is mounted at an outer side of the engine block (2).

6. An internal combustion engine (1) according to claim 4 or 5, wherein the electric motor (20, 28) has an output shaft which is drivably coupled to the drive shaft (17), whereas the output shaft and the drive shaft (17) are angled with respect to each other.

7. An internal combustion engine (1) according to any one of the claims 4-6, wherein the engine (1) is provided with a starter motor (28) for starting the engine (1), wherein the electric motor (20) and the starter motor (28) form an integral drive motor (20, 28) for driving either the crankshaft (3) upon starting the engine (1) or the drive shaft (17) after the engine (1) has been started, wherein an output shaft of the integral drive motor (20, 28) is coupled to the crankshaft (3) through a freewheel mechanism (30), on the one hand, and to the drive shaft (17) through a controllable clutch (32), on the other hand.

8. An internal combustion engine (1) according to any one of the preceding claims and claim 2, wherein the engine (1) is provided with a spring (26) between the engine block (2) and at least one of the first and second external gears (18, 19), which spring (26) exerts a force between the engine block (2) and the at least one of the first and second external gears (18, 19) in longitudinal direction of the drive shaft (17) and the adjusting shaft (15).

9. An internal combustion engine (1) according to claim 8, wherein the spring (26) has a ring shape and extends about one of the first and second external gears (18, 19).

10. An internal combustion engine (1) according to claim 9, wherein the spring is a wave spring (26).

Drawing