Crank Drive for a Reciprocating-Piston Engine and a Reciprocating Piston Engine with Such a Crank Drive

Abstract

A crank drive for a reciprocating-piston engine includes a crankshaft which has at least one crank pin. At least one eccentric is rotatably arranged on the crank pin via which at least one connecting rod is to be rotatably mounted on the crank pin. A piston can be arranged so as to move in a translatory fashion in a cylinder having a variable compression ratio of the reciprocating-piston engine and can be coupled in an articulated fashion via the connecting rod to the crankshaft. At least one actuator shaft is arranged coaxially with respect to the crankshaft, by which actuator shaft the eccentric can be rotated relative to the crank pin by driving the actuator shaft. As a result, the compression ratio of the cylinder can be adjusted. An actuator element, by which the actuator shaft can be driven, is arranged at one end of the crankshaft and adjoins the actuator shaft in the axial direction of the crankshaft.

Claims

1. A crank drive for a reciprocating piston engine, comprising: a crankshaft having at least one crankpin journal; at least one eccentric arranged rotatably on the crankpin journal and via which a connecting rod is mounted rotatably on the crankpin journal, by which connecting rod a piston arrangeable so as to move translationally in a cylinder having a variable compression ratio is couplable to the crankshaft in an articulated manner; at least one actuating shaft arranged coaxially with respect to the crankshaft and via which the eccentric is rotatable relative to the crankpin journal by driving the actuating shaft, as a result of which the compression ratio of the cylinder is settable; and an actuator by which the actuating shaft is driven, wherein the actuator is arranged at one end of the crankshaft and adjoins the crankshaft in an axial direction of the crankshaft.

2. The crank drive according to claim 1, wherein the actuating shaft penetrates at least one main bearing journal of the crankshaft completely in the axial direction of the crankshaft.

3. The crank drive according to claim 2, wherein the at least one main bearing journal is the last main bearing journal of the crankshaft in the axial direction of the crankshaft.

4. The crank drive according to claim 1, wherein the actuator is arranged coaxially with respect to the crankshaft.

5. The crank drive according to claim 1, wherein the actuator is rotatable about a rotational axis relative to the crankshaft, in order to drive the actuating shaft.

6. The crank drive according to claim 4, wherein the rotational axis of the actuator coincides with a crankshaft rotational axis about which the crankshaft is rotatable relative to a crankcase during operation of the reciprocating piston engine.

7. The crank drive according to claim 5, wherein the actuator corotates with the crankshaft permanently about the rotational axis, while the crankshaft rotates about its crankshaft rotational axis and an adjustment of the compression ratio is not carried out.

8. The crank drive according to claim 7, wherein the actuator corotates with the crankshaft permanently about the rotational axis at a fixed rotational speed ratio to the crankshaft, while the crankshaft rotates about its crankshaft rotational axis and an adjustment of the compression ratio is not carried out.

9. The crank drive according to claim 5, wherein a rotation of the actuator about the rotational axis is not carried out, while the crankshaft rotates about its crankshaft rotational axis and an adjustment of the compression ratio is not carried out.

10. The crank drive according to claim 1, wherein the actuator is configured as an internal gear of a planetary gear mechanism which has the internal gear, a sun gear, a planetary carrier and at least one planetary gear which meshes with the sun gear and with the internal gear and is mounted rotatably on the planetary carrier.

11. The crank drive according to claim 10, wherein the planetary carrier is connected fixedly to the crankshaft so as to rotate with the crankshaft.

12. The crank drive according to claim 10, wherein the sun gear is connected fixedly to the actuating shaft so as to rotate with the actuating shaft.

13. The crank drive according to claim 10, wherein a worm drive is provided by which the internal gear is driven and is rotated as a result by way of which the actuating shaft is driven.

14. A reciprocating piston engine for a motor vehicle, comprising: at least one cylinder which has a variable compression ratio; a crankcase; and a crank drive comprising: at least one piston which is received in the cylinder such that the piston is movable translationally; at least one connecting rod which is coupled to the piston in an articulated manner; a crankshaft having at least one crankpin journal and having at least one main bearing journal, via which the crankshaft is mounted on the crankcase such that the crankshaft is rotatable relative to the crankcase about a crankshaft rotational axis; at least one eccentric which is arranged rotatably on the crankpin journal and via which the connecting rod is mounted rotatably on the crankpin journal, as a result of which the piston is coupled to the crankshaft in an articulated manner; at least one actuating shaft which is arranged coaxially with respect to the crankshaft and via which the eccentric is rotatable relative to the crankpin journal by way of driving of the actuating shaft, as a result of which the compression ratio of the cylinder is settable; and an actuator, by which the actuating shaft is driven, wherein the actuator is arranged at one end of the crankshaft and adjoins the crankshaft in the axial direction of the crankshaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a diagrammatic side view of a crank drive according to the invention for a reciprocating piston engine in accordance with a first embodiment.

[0031] FIG. 2 shows details of a diagrammatic side view of the crank drive in accordance with a second embodiment.

[0032] In the figures, identical or functionally identical elements are provided with identical designations.

DETAILED DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 shows a diagrammatic side view of a first embodiment of a crank drive 1 for a reciprocating piston engine, in particular of a motor vehicle. The motor vehicle is configured, for example, as a car, in particular as a passenger car, and can be driven by means of the reciprocating piston engine. Here, the reciprocating piston engine is configured as an internal combustion engine or as a combustion engine, and comprises at least one combustion chamber which is configured as a cylinder. In particular, the reciprocating piston engine has a plurality of cylinders. Moreover, the reciprocating piston engine has a crankcase which is configured, for example, as a cylinder crankcase and by way of which, for example, the cylinders are formed. As will be described in greater detail in the following text, the respective cylinder has a variable compression ratio, the value of which changes and can therefore be set. Per cylinder, for example, the crank drive 1 has a piston which is not shown in the figure, is received in the respective cylinder such that it can be moved translationally, and can move to and fro translationally in the cylinder. During combustion operation of the reciprocating piston engine, the respective cylinder is supplied with fuel, in particular liquid fuel, for operating the reciprocating piston engine and with air, with the result that fuel/air mixtures are produced in the respective cylinder. The respective fuel/air mixtures are ignited and burned as a result, by way of which the relative cylinder is driven, that is to say is moved translationally relative to the crankcase.

[0034] Here, per piston, the crank drive 1 comprises a connecting rod which is coupled to the respective piston in an articulated manner, is not shown in the figures, and is coupled to the respective piston in an articulated manner, for example, via a gudgeon pin. As a result, the translational movements of the piston can be transmitted to the respective connecting rod.

[0035] Moreover, the crank drive 1 comprises a crankshaft 2 which has a plurality of main bearing journals 3, 3 and 3 which in the axial direction of the crankshaft 2 are arranged such that they are spaced apart from one another and follow one another. Via the main bearing journals 3, 3 and 3, the crankshaft 2 is mounted rotatably on the crankcase, with the result that the crankshaft 2 can rotate relative to the crankcase about a crankshaft rotational axis 4. This rotatability of the crankshaft 2 about the crankshaft rotational axis 4 relative to the crankcase is illustrated by way of an arrow 5 in FIG. 1.

[0036] Furthermore, in particular per cylinder, the crankshaft 2 has a crankpin journal 6 or 6 which is arranged eccentrically with respect to the crankshaft rotational axis 4 and therefore carries out a stroke when the crankshaft 2 rotates relative to the crankcase about the crankshaft rotational axis 4. Here, an eccentric 7 or 7 is mounted or arranged rotatably on the respective crankpin journal 6 or 6, with the result that the respective eccentric 7 or 7 can rotate about an eccentric rotational axis 8 relative to the respective crankpin journal 6 or 6. It can be seen particularly clearly from FIG. 1 that the eccentric rotational axis 8 runs at least substantially parallel to the crankshaft rotational axis 4 and is spaced apart or offset here from the crankshaft rotational axis 4.

[0037] Via the respective eccentric 7 or 7, the respective connecting rod is mounted rotatably on the respective crankpin journal 6 or 6, as a result of which the piston is coupled in an articulated manner to the respective crankpin journal 6 or 6 and therefore to the crankshaft 2 overall via the gudgeon pin, the connecting rod and the respective eccentric 7 or 7. By way of said articulated coupling of the respective piston to the crankshaft 2, the respective translational movements of the respective piston can be converted into a rotational movement of the crankshaft 2 about its crankshaft rotational axis 4. If, as described above, the respective piston is therefore driven, the crankshaft 2 is driven as a consequence and is therefore rotated about its crankshaft rotational axis 4 relative to the crankcase. As a result, the reciprocating piston engine can provide torques for driving the motor vehicle via the crankshaft 2 in combustion operation.

[0038] Furthermore, the crank drive 1 comprises at least one actuating shaft 9 which is arranged coaxially with respect to the crankshaft 2 or with respect to the crankshaft rotational axis 4 and via which the respective eccentric 7 or 7 can be turned relative to the respective crankpin journal 6 or 6 by way of driving of the actuating shaft 9. As a result, the compression ratio of the respective cylinder can be set. Moreover, at least one actuator 10 which is also called an actuating element is provided, by means of which the actuating shaft 9 can be driven. By way of driving of the actuating shaft 9, the latter is rotated about an actuating shaft rotational axis 11, in particular relative to the crankshaft 2 and relative to the crankcase, the actuating shaft rotational axis 11 coinciding with the crankshaft rotational axis 4. By way of rotation of the actuating shaft 9 about the actuating shaft rotational axis 11, the respective eccentric 7 or 7 is turned about the eccentric rotational axis 8 relative to the respective crankpin journal 6 or 6, as a result of which the compression ratio of the respective cylinder is changed. Here, the compression ratio is changed in such a way that the respective eccentric 7 or 7, in particular its outer circumferential-side shell face, is of eccentric configuration with regard to the eccentric rotational axis 8. Here, the eccentric rotational axis 8 coincides, for example, with a center axis of the respective crankpin journal 6 or 6. If the respective eccentric 7 or 7 is therefore rotated about the eccentric rotational axis 8 relative to the respective crankpin journal 6 or 6, the respective connecting rod and therefore the respective piston are displaced as a result in the radial direction of the respective crankpin journal 6 or 6 relative to the respective crankpin journal 6 or 6, as a result of which, for example, a stroke height of the piston and therefore the respective compression ratio of the respective cylinder are set or changed.

[0039] Here, for example, the respective eccentric 7 or 7 is configured as an eccentric bearing shell, via which the respective connecting rod is mounted rotatably on the respective crankpin journal 6 or 6. It can be seen from FIG. 1, in particular, that the main bearing journals 3, 3 and 3 are connected to the crankpin journals 6 and 6 via respective crank webs 14. In order for it to be possible for the respective eccentric 7 or 7 to be turned relative to the crankpin journal 6 or 6, the respective eccentric 7 or 7 has, for example, a toothing system 12 or 12 which is configured as an external toothing system and the function of which will be described in greater detail in the following text.

[0040] In order for it then to be possible for excessive weakening of the crankshaft 2 which is brought about by way of the use of the variable compression ratio to be avoided and, as a consequence, for particularly efficient and therefore low-emissions and low-fuel consumption operation of the reciprocating piston engine to be realized, the actuator 10 is arranged at one end 13 of the crankshaft 2 and adjoins the crankshaft 2, in particular the end 13, in the axial direction of the crankshaft 2. Here, the axial direction of the crankshaft 2 coincides with the crankshaft rotational axis 4.

[0041] It can be seen from FIG. 1 that the actuating shaft 9 is connected fixedly with a gearwheel 15 so as to rotate with it, which gearwheel 15 meshes with the toothing system 12 and therefore with the eccentric 7. If the actuating shaft 9 is therefore rotated about the actuating shaft rotational axis 11, in particular relative to the crankshaft 2, the eccentric 7 is driven by the gearwheel 15 and, as a result, is turned about the eccentric rotational axis 8 relative to the crankpin journal 6.

[0042] The actuating shaft 9 is also called a synchronizing shaft. Here, the crank drive 1 comprises a further synchronizing shaft 16 which is also called an actuating shaft, is connected fixedly to gearwheels 17 and 18 so as to rotate with them, and can be rotated about the actuating shaft rotational axis 11, in particular relative to the crankshaft 2. Here, the synchronizing shaft 16 is also arranged coaxially with respect to the crankshaft 2. The gearwheel 17 meshes with the toothing system 12 which is configured as an external toothing system and therefore with the eccentric 7, with the result that, when the eccentric 7 is rotated about the eccentric rotational axis 8 relative to the crankpin journal 6, the gearwheel 17 and the synchronizing shaft 16 are rotated about the actuating shaft rotational axis 11 relative to the crankshaft 2. Here, the gearwheel 18 is also rotated about the actuating shaft rotational axis 11 relative to the crankshaft 2, since the gearwheel 18 is connected fixedly to the synchronizing shaft 16 so as to rotate with it. Here, the gearwheel 18 meshes with the toothing system 12 which is configured as an external toothing system, and therefore with the eccentric 7, with the result that the eccentric 7 is turned about the eccentric rotational axis 8 relative to the crankpin journal 6 by way of rotation of the gearwheel 18 about the actuating shaft rotational axis 11 relative to the crankshaft 2. The eccentrics 7 and 7 are therefore coupled to one another via the gearwheels 17 and 18 and the synchronizing shaft 16, in particular are coupled fixedly to one another so as to rotate together, with the result that the eccentrics 7 and 7 are rotated at the same time or synchronously about the eccentric rotational axis 8 relative to the crankpin journals 6 and 6 when the actuating shaft 9 is rotated by means of the actuator 10 about the actuating shaft rotational axis 11, in particular relative to the crankshaft 2. The actuating shaft 9 is therefore a synchronizing shaft which is provided in addition to the synchronizing shaft 16 and to which the actuator 10 which is arranged at the end 13 which is also called the crankshaft end is attached, in particular at least indirectly.

[0043] It can be seen from FIG. 1 that the actuating shaft 9 runs in the center of the main bearing journal 3 and in the process penetrates the main bearing journal 3 completely in the axial direction of the crankshaft 2. This means that the actuating shaft 9 protrudes out of or protrudes beyond the main bearing journal 3 at both ends or on both sides in the axial direction of the crankshaft 2. Here, the main bearing journal 3 is the last main bearing journal of the crankshaft 2 in the axial direction of the crankshaft 2, in particular on the side of the end 13. At that end 19 of the crankshaft 2 which lies opposite the end 13 in the axial direction of the crankshaft 2, said crankshaft 2 has the main bearing journal 3. Here, the synchronizing shaft 16 is arranged in the center of the main bearing journal 3 and penetrates the latter completely in the axial direction of the crankshaft 2. As a result, excessive weakening of the crankshaft 2 can be avoided.

[0044] Furthermore, it can be seen particularly clearly from FIG. 1 that the actuator 10 is arranged coaxially with respect to the crankshaft 2, and can be rotated here about a rotational axis 20, in particular relative to the crankshaft 2 and/or relative to the crankcase. Here, the rotational axis 20 of the actuator 10 coincides with the crankshaft rotational axis 4, the rotational axis 20 of the actuator 10 also being called the actuator rotational axis. It can be seen overall that the crankshaft rotational axis 4, the actuating shaft rotational axis 11 and the rotational axis 20 of the actuator 10 coincide. In order to set the compression ratio and therefore to rotate the eccentric 7 and 7, the actuator 10 is rotated about the rotational axis 20 (actuator rotational axis), in particular relative to the crankshaft 2 and/or relative to the crankcase.

[0045] In the case of the first embodiment which is shown in FIG. 1, the actuator is configured as a non-rotating, rotatable actuator which, although it can be rotated or is rotated about the rotational axis 20, in order to change the compression ratio, a rotation of the actuator 10 about the rotational axis 20 is not carried out while the crankshaft 2 rotates about the crankshaft rotational axis 4, and the compression ratio remains constant or an adjustment of the compression ratio is not carried out. Therefore, for example, the actuator 10 rotates about the rotational axis 20 only for rotating the eccentrics 7 and 7, that is to say only for adjusting the compression ratio. In the case of the refinement of the actuator 10 as a non-rotating actuator, advantageous, correct relative rotational speeds can be ensured, and the actuator 10 is at a standstill in the case of a constant compression ratio.

[0046] Furthermore, in the case of the first embodiment, the actuator 10 is configured as an internal gear 21 of a planetary gear mechanism 22. Here, the planetary gear mechanism 22 comprises the internal gear 21 (actuator 10), a sun gear 23, a planetary carrier 24 which is also called a spider, and at least one or more planetary gears 25 which mesh with the sun gear 23 and with the internal gear 21 and are mounted rotatably on the planetary carrier 24. Here, the internal gear 21 has a first toothing system in the form of an internal toothing system 26 which meshes with the planetary gears 25. Here, the planetary carrier 24 is configured fixedly with respect to the crankshaft, that is to say is connected fixedly to the crankshaft 2 so as to rotate with it. The sun gear 23 is connected fixedly to the actuating shaft 9 so as to rotate with it, with the result that the actuating shaft 9 and therefore the gearwheel 15 are rotated about the rotational axis 20 or about the actuating shaft rotational axis 11, in particular relative to the crankshaft 2 and/or relative to the crankcase, by way of rotation of the sun gear 23 about the rotational axis 20. Therefore, the sun gear 23 is rotated about the rotational axis 20 in order to adjust the compression ratio. To this end, the internal gear 21 is in turn rotated about the rotational axis 20.

[0047] In order to rotate the internal gear 21 about the rotational axis 20, a drive 27 is provided, by means of which the internal gear 21 can be driven and, as a result, can be rotated about the rotational axis 20. In the case of the first embodiment which is illustrated in FIG. 1, the drive 27 is configured as a worm drive which has what is known as a worm 28. The worm 28 can be rotated about a worm rotational axis 29 relative to the crankcase and, in particular, relative to the crankshaft 2, the worm rotational axis 29 running perpendicularly with respect to an imaginary plane, and the rotational axis 20 lying in the imaginary plane or running parallel to the imaginary plane. Furthermore, the worm drive comprises a worm gear 30 which meshes with the worm 28 and, as a result, can be rotated about the rotational axis 20, such that the worm 28 is rotated about the worm rotational axis 29. It can be seen here from FIG. 1 that the worm gear 30 is formed by way of the internal gear 21. To this end, for example, the internal gear 21 has a second toothing system in the form of an external toothing system 31 which is configured, for example, as a helical toothing system. Here, the worm 28 meshes with the external toothing system 31 or engages into the external toothing system 31, with the result that, as is generally known from worm drives or worm gear mechanisms, the worm gear 30 or the internal gear 21 is rotated about the rotational axis 20 when the worm 28 is rotated about the worm rotational axis 29. This is illustrated by way of a double arrow 32 in FIG. 1.

[0048] In order to drive and therefore rotate the worm 28 about the worm rotational axis 29, for example, a motor which cannot be seen in the figures is provided which is configured, for example, as an electric motor. The use of the worm drive is advantageous in so far as the worm drive has a self-locking action or enters into a self-locking state when the worm 28 is not rotated actively about the worm rotational axis 29 by means of the motor. As a result, in the case of a constant compression ratio, the internal gear 21 does not have to be secured by way of additional and separate actuators or brakes against an undesired rotation about the rotational axis 20 by means of the worm drive, with the result that an undesired change of the compression ratio can be avoided by way of the self-locking action of the worm drive and therefore in a particularly inexpensive manner.

[0049] FIG. 2 shows a second embodiment of the crank drive 1. The second embodiment differs, in particular, from the first embodiment in that the actuator 10 is not configured as a rotatable, non-rotating actuator, but rather as a rotatable, rotating actuator, which is illustrated by way of an arrow 33 in FIG. 2. The rotatable, rotating actuator 10 is to be understood to mean that the actuator corotates permanently with the crankshaft 2 about the rotational axis 20, in particular with a fixed rotational speed ratio to the crankshaft 2, while the crankshaft 2 rotates about its crankshaft rotational axis 4, and an adjustment of the compression ratio is not carried out. Here, furthermore, a relative rotation between the actuator 10 and the crankshaft 2 is not carried out, for example. In order to change the compression ratio, the actuator 10 is turned about the rotational axis 20 relative to the crankshaft 2. If, however, the compression ratio remains constant, the actuator 10 rotates with the crankshaft 2 about the rotational axis 20. This results in a wide variety of control options; respective rotational speed ratios which are set should be compatible, however, with the overall mechanism, in particular with regard to plain bearings.

LIST OF DESIGNATIONS

[0050] 1 Crank drive [0051] 2 Crankshaft [0052] 3, 3, 3 Main bearing journal [0053] 4 Crankshaft rotational axis [0054] 5 Arrow [0055] 6, 6 Crankpin journal [0056] 7, 7 Eccentric [0057] 8 Eccentric rotational axis [0058] 9 Actuating shaft [0059] 10 Actuator [0060] 11 Actuating shaft rotational axis [0061] 12, 12 External toothing system [0062] 13 End [0063] 14 Crank web [0064] 15 Gearwheel [0065] 16 Synchronizing shaft [0066] 17 Gearwheel [0067] 18 Gearwheel [0068] 19 End [0069] 20 Rotational axis [0070] 21 Internal gear [0071] 22 Planetary gear mechanism [0072] 23 Sun gear [0073] 24 Planetary carrier [0074] 25 Planetary gear [0075] 26 Internal toothing system [0076] 27 Drive [0077] 28 Worm [0078] 29 Worm rotational axis [0079] 30 Worm gear [0080] 31 External toothing system [0081] 32 Double arrow [0082] 33 Arrow

[0083] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.