The invention relates to a method and device for reducing rotational non-uniformities of the crankshaft of an internal combustion piston engine.
A characteristic of the rotation of the crankshaft of internal combustion piston engines, in particular reciprocating-piston internal combustion engines, is that this rotation, which is generated by the working cycles of the piston(s) connected to the crankshaft, is non-uniform. This non-uniformity increases when the number of cylinders is reduced, when rotational speeds are low, and at high loads. In practice, it is attempted to counteract these rotational non-uniformities by using large flywheel masses, which are connected, if necessary, with the crankshaft in a manner having a low torsion constant. A further attempt to counteract the rotational non-uniformities is to connect a cam disk with the crankshaft in a torque-proof manner, which cam disk is followed by a follower member that is moveable against a spring force. During phases in which the angular speed of the crankshaft is to be reduced, the follower member is moved towards the spring, so that potential energy is stored therein. This potential energy can be stored back in the rotation of the crankshaft during phases in which the angular speed of the crankshaft is to be increased. Despite all previously-existing measures, engines with few cylinders, e.g., four or fewer cylinders, exhibit comfort disadvantages as compared to high-cylinder engines, which disadvantages adversely affect their acceptability. In view of the increasing importance of low fuel consumption, a so-called “downsizing” of the engines is desired, which downsizing necessarily leads to a reduced number of cylinders due to the minimum volume of the individual cylinders, which minimum volume is dictated by thermodynamic reasons.
A drivable shaft having a moment of inertia that is variable in an acceleration-dependent manner is known from DE 196 49 712 C2. An inertial mass, which moves counter to the rotational direction of the shaft from an idle position relative to the shaft to a displaced position when the rotation of the shaft is accelerated, moves flywheel mass elements via transmission means during its displacement movement towards a reduction of the radial distance from the rotational axis; the flywheel mass elements are connected to the shaft in a torque-proof manner and are movably guided approximately radially relative to the rotational axis. The inertial mass is formed as an inertial ring extending concentrically around the shaft, which inertial ring is connected with each flywheel mass element via the transmission means. If, starting at a state in which the flywheel mass elements are spaced a large distance from the shaft, the rotational speed of the shaft increases, the inertial ring lags behind the shaft, so that the distance between the flywheel mass elements and the shaft decreases. Consequently, the moment of inertia of the assembly decreases when the shaft accelerates, which boosts the acceleration of the shaft. When the rotational speed of the shaft decreases, the moment of inertia of the assembly increases, whereby the reduction of the rotational speed is boosted. All in all, this assembly achieves an improved response behavior of the internal combustion engine by reducing the effective moment of inertia.
It is an object of the invention to provide a method and device, with which the rotational non-uniformities of the crankshaft can be considerably reduced, also in internal combustion piston engines having a low number of cylinders, so that internal combustion piston engines having a low number of cylinders, e.g., four or fewer cylinders, exhibit a running comfort that is acceptable to demanding customers.
The part of the invention object that relates to the method is achieved by a method according to claim 1.
Dependent claims 2 and 3 are directed to advantageous ways of implementing the inventive method.
Claim 4 identifies the basic embodiment of an inventive device for achieving the part of the invention object concerning the device.
The dependent claims, which refer back to claim 4, are directed to advantageous embodiments and further developments of the inventive device.
The basic idea of the invention is to draw off energy and/or power from the crankshaft and to store it in the compensating mass element during phases in which the crankshaft supplies a high torque. During phases in which the crankshaft supplies little torque or must be driven itself, because the piston(s) connected to the crankshaft is(are) performing compression work or discharge work, the energy stored in the compensating mass element is returned. By directly storing kinetic energy in the compensating mass element, no complex energy conversions are necessary and the invention operates with high efficiency.
The invention will be explained below, exemplarily and in further detail, with the assistance of schematic figures.
FIGS. 1 and 2 depict end views of an inventive device in different operating states,
FIG. 3 depicts torque curves of a 4-cylinder, four-stroke, spark-ignition engine for illustrating the invention,
FIG. 4 depicts a table that shows alternating torques for different types of engines,
FIG. 5 depicts a schematic end view of an inventive device, which is modified with regard to FIG. 1,
FIG. 6 depicts a schematic view of a piston-cylinder unit,
FIG. 7 depicts a schematic end view of a modified embodiment of the inventive device, similar to FIGS. 1 and 2,
FIG. 8 depicts a schematic diagram of an embodiment of an adjusting device and
FIG. 9 depicts a sketch for explaining a mass compensator.
According to FIG. 1, which shows an end view of an inventive device, a crankshaft 10 of an internal combustion piston engine having a known structure comprises a radially-protruding driver extension 12 that is connected in a torque-proof manner with, or is formed integrally with, the crankshaft 10. A compensating mass element 14 is supported on the crankshaft 10 adjacent to the driver extension 12, which compensating mass element is advantageously balanced with regard to the rotational axis A of the crankshaft 10.
Axially adjacent to the compensating mass element 14, a bearing shield 16 (shaded; the axial arrangement is not visible in FIG. 1) is supported on a not-illustrated crankcase so as to be pivotable about an axis B that is spaced from the rotational axis A of the crankshaft. The bearing shield 16 has a through-hole 20, through which the crankshaft 10 extends, so that the above-described component assembly can be disposed at a terminal end of the crankshaft or in a central region of the crankshaft. The pivot axis B is parallel to the rotational axis A of the crankshaft. A guide coupler 22 with a radially protruding arm 24 is rotatably supported on the bearing shield 16 that is pivotable relative to the crankshaft.
The radial arm is connected to the driver extension 12 via a connecting member 26 and is connected via a further connecting member 28 with the compensating mass element 14 in a hinge 29. Advantageously, the connecting members 26 and 28 are coaxially hinged to the arm 24 of the guide coupler 22. The connecting member 28, for example, projects into a radial slot (not illustrated) of the compensating mass element 14 and is supported therein by a pin. The pivot axes of the hinges, about which the connecting members are pivotable relative to each other and are pivotable relative to the driver extension 12, the guide coupler 22 and the compensating mass element 14, are parallel to each other and are parallel to the axes A and B.
By pivoting the bearing shield 16 about the crankcase-mounted bearing having the axis B, the spacing between the rotational axis C, about which the guide coupler 22 rotates, and the rotational axis A of the crankshaft can be changed. An adjusting device, identified as a whole by 40, is provided for pivoting the bearing shield 16, which adjusting device 40 includes an adjusting member 42 connected to an arm 44 in a hinged manner, which arm 44 is rigidly connected to the bearing shield 16. Approximately in the direction of extension of the arm 44, the bearing shield 16 has another arm 46 on its opposite side, which is rigidly connected therewith and is pivotable about the pivot axis B. The adjusting member 42 can be moved in the vertical direction according to FIG. 1 in a known manner using a hydraulic cylinder or an electric motor, wherein the moveability is advantageously limited by stops 48 and 50.
The above-described device can be constructed in a highly compact manner with an interleaved construction. The compensating mass element 14 is rotatably supported on the crankshaft between the guide coupler 22 and the driver extension 12 and coaxially with the rotational axis A of the crankshaft. The guide coupler 22 is supported so as to be rotatable about the rotational axis C that is defined by the bearing shield 16. Axially adjacent to the guide coupler 22, the arms 44 and 46 of the bearing shield 16 extend. It is understood that the eccentric pivotability of the bearing shield 16 relative to the crankshaft and its adjustment can also be provided by other constructions, e.g., by supporting the bearing shield directly with a pin in the crankcase, which pin is disposed eccentric to the rotational axis of the crankshaft.
FIG. 1 illustrates the state of the assembly wherein the rotational axis C of the guide coupler 22 is maximally spaced from the rotational axis A of the crankshaft 10. Advantageously, the connecting line between the rotational axes A and C is parallel to the moving direction of the not-illustrated pistons of the internal combustion engine, which are connected to the crankshaft 10, and is aligned in the illustrated view with the line of movement of the pistons. Minor directional changes of the connecting line during pivoting of the bearing shield 16 about the pivot axis B need not be considered. The arrangement of the driver extension 12, the radial arm 24 and the connecting members 26 and 28 is such that the connecting members 26 and 28 pass through their extended position twice during one revolution of the crankshaft 10 or during the revolution of the guide coupler 22 that is eccentric therewith, so that the compensating mass 14 of the crankshaft 10 advances and lags, respectively, twice during one revolution, i.e. rotates at a higher and a lower speed, respectively, than the crankshaft. The advancement and lag, respectively, can be adapted to the particular requirements by the geometrical arrangement of the connecting members.
FIG. 2 shows the state of the assembly of FIG. 1 wherein the rotational axes A and C coincide; that is, the state of maximal eccentricity according to FIG. 1 has been shifted to the state of minimal eccentricity in which the guide coupler 22 rotates coaxially with the crankshaft 10. In this state, the relative positioning of the driver extension and the connecting members 26 and 28 and the radial arm 24 remains constant, so that the compensating mass element 14 always rotates at the same angular speed as the crankshaft 16.
In contrast thereto, in the position according to FIG. 1, the compensating mass element 14 must be cyclically accelerated and decelerated, so that the crankshaft must apply additional torque to the compensating mass element during phases of rotation in which the compensating mass element is accelerated, and the crankshaft receives an additional torque from the compensating mass element during other phases of rotation, in which the angular speed of the compensating mass element is reduced relative to the crankshaft.
FIG. 3
a) shows an exemplary torque curve of a charged, 4-cylinder, spark-ignition engine that is operated in the four stroke process and rotates at a speed of, for example, 1000 rpm at full load. The abscissa indicates the rotational position of the crankshaft in degrees, and the ordinate indicates the torque from the crankshaft, which torque is acting in the drive train of the vehicle. The torque fluctuations are larger at increasing loads and become increasingly noticeable in an unpleasant manner in the drive train when the rotational speed decreases, whether it is due to acceleration fluctuations of the entire vehicle or due to noises or vibrations, all of which are perceptible by the vehicle occupants in a comfort-reducing manner.
Part b) of FIG. 3 shows the torque that is producible by the above-described inventive device and is applyable from the compensating mass 14 to the crankshaft 10. As can be seen, a negative torque is necessary for accelerating the compensating mass element during phases in which the crankshaft generates a high positive torque and, conversely, the compensating mass element supplies a positive torque to the crankshaft in the phases during deceleration in which the crankshaft supplies a negative torque due to the pistons. In summary, by equipping a known internal combustion engine with the inventive device, an overall torque, which is illustrated in FIG. 13c and whose fluctuations are considerably reduced as compared to the torque fluctuations of FIG. 3a, results at the crankshaft. Hence, a very comfortable, even speed of the internal combustion piston engine is achieved with the inventive device, even when it has a low number of cylinders. It is pointed out that FIG. 3 shows the torque fluctuations. In particular in illustrations a and c, the curves must be shifted upwards by the average torque that is supplied by the crankshaft to the vehicle. By pivoting the bearing shield 16, the device can be adjusted to the respective compensation requirements. At high fluctuations, it is therefore operated with high eccentricity and/or with a large distance between the rotational axes A and C. At low fluctuations, the eccentricity is decreased.
FIG. 4 shows in tabular form the main orders of the alternating torques shown in FIG. 3a), which must be compensated, for internal combustion engines having different numbers of cylinders and different operating principles (two-stroke process, four-stroke process).
The arrangement shown in FIGS. 1 and 2 is suitable for reducing torque fluctuations at the crankshaft for the second order of a 2-cylinder two-stroke engine or a 4-cylinder four-stroke engine.
In the embodiment of the inventive device according to FIG. 5, the eccentric movement and/or the stroke movement of the guide coupler 22 relative to the crankshaft 10 is converted into a relative rotation between the compensating mass element 14 and the crankshaft 10 by pivoting the connecting member 52. This pivoting takes place once during each revolution of the crankshaft, so that the embodiment according to FIG. 5 is suitable for reducing torque variations at the crankshaft for the first order in a 1-cylinder two-stroke engine or a 2-cylinder four-stroke engine.
The inventive device can also be used for compensating torque fluctuations and/or rotational non-uniformities at the crankshaft of other engines, e.g., 3-cylinder engines, in which, for example, the driver extension 12 is not rigidly connected with the crankshaft, but rather is connected with the crankshaft via a speed-increase gear unit or speed-decrease gear unit, as a result of which the driver extension rotates at a speed suitable for compensating torque fluctuations, e.g., in a 3-cylinder engine having a rotational speed increased by the factor 1.5 in comparison to the embodiment of the respective device for a 2-cylinder engine.
FIG. 6 schematically shows a piston 60 of a cylinder of a reciprocating-piston internal combustion engine, which is connected with the crankshaft 10 via a piston rod 62 in a known manner. During four-stroke operation, only one working stroke takes place in a known manner during two revolutions of the crankshaft; a driving torque MK is applied to the crankshaft 10 by the piston 60 in the working stroke. The inclination of the piston rod 62 relative to the vertical line results in that the piston 60 is braced on the cylinder wall by lateral forces. These lateral forces can be compensated by applying a counter moment FN×s(t) to the engine block.
FIG. 7 shows an example of how such a counter moment is applied to the engine block. For this purpose, the assembly according to FIG. 1 is augmented in the illustrated example such that the compensating mass element 14 is provided with a circumferential toothing 64, and a further compensating mass element 66 is supported on the crankcase so as to be rotatable about an axis D, which is spaced from the rotational axis A of the crankshaft; the compensating mass element 66 is formed with a circumferential toothing 68 whose diameter is half the diameter of the circumferential toothing 64. Thus, the other compensating mass element 66 rotates at a speed that is twice the speed of the compensating mass element 14, wherein it fully experiences the rotational non-uniformities of the compensating mass element 14. In this way, the additional compensating mass element 66 can be used for generating a counter moment that compensates the lateral piston forces, according to FIG. 6, in the illustrated example for a 4-cylinder four-stroke engine.
At this point, it is again pointed out that the compensating mass element 14 and the additional compensating mass element 66 are advantageously balanced with regard to their rotational axes. They can be formed as disk-shaped or in other ways. The additional compensating mass element 66 may be used for a known two-shaft compensation of the second order for the free inertial forces. In contrast to the conventional dampening of rotational non-uniformities using a flywheel, according to the invention the angular speed of the compensating mass element is systematically changed substantially in phase with the angular speed of the crankshaft. Consequently, the moment of inertia of the compensating mass element can be smaller than that of conventional flywheels, so that the engine responds well to position changes of the accelerator pedal.
FIG. 8 schematically shows a particularly simple embodiment of an adjusting device 40. The arm 44 of the bearing shield 16 (FIG. 1) is connected in a hinged manner to a shaft of a piston 72 of a double-acting piston cylinder unit, which shaft serves as an adjusting member 42; the pressure chambers of said piston cylinder unit are connected with each other via two conduits 76 and 78. A one-way valve 80 and 82 is arranged in each of the conduits 76 and 78, wherein the one-way valves 80 and 82 act oppositely to each other. Further, a shutoff valve 84 and 86 is disposed in each respective conduit.
Due to the eccentric bearing of the bearing shield 16, alternating forces act on the arm 44 during each revolution of the compensating mass element 14, which forces are directed upwards or downwards according to the figures. Depending on the opening of one of the shutoff valves 84 or 86, a hydraulic fluid located in the piston cylinder unit 74 can only flow from one pressure chamber into the other one, so that a displacement in the one or the other direction takes place by correspondingly controlling the shutoff valves 84 and 86, without the need for an external source of pressurizing medium. It is understood that a suitable re-filling mechanism for hydraulic fluid ensures that the conduits and the piston cylinder unit are constantly filled with hydraulic fluid and are free from air.
With the help of FIG. 9, a possibility is explained of how, according to the invention, not only rotational non-uniformities of the crankshaft can be compensated, but also how a mass compensation can be carried out in a 1-cylinder two-stroke engine or in a 2-cylinder four-stroke engine. The compensating mass element of FIG. 9, which is denoted with 14, corresponds to the compensating mass element 14 of the embodiment according to FIG. 5, whose remaining components are not illustrated in FIG. 9 for the sake of simplicity. The compensating mass element 14 has a circumferential toothing 64 that meshes with a circumferential toothing 68 of another compensating mass element 88. Reference numerals 90 and 92 denote unbalanced masses of the compensating mass elements; that is, in contrast to the preferred embodiment, the compensating mass element 14 is not balanced relative to its rotational axis, but rather has a specific unbalanced mass 90. The unbalanced masses 90 and 92 are preferably equal and arranged such that they are each located simultaneously in the vertical position according to FIG. 5, i.e. they simultaneously pass the top dead center and the bottom dead center, and are disposed in opposite phase in their horizontal positions. As was already explained with the help of FIG. 5, this arrangement is also preferably used for compensating rotational non-uniformities of the crankshaft of a 1-cylinder two-stroke engine or 2-cylinder four-stroke engine. When the unbalanced masses are arranged relative to the piston of a 1-cylinder two-stroke engine or the pistons of a 2-cylinder four-stroke engine such that they are located in the bottom dead center when the piston(s) is/are located in the top dead center, a mass compensation can be achieved for said engines with the arrangement according to FIG. 5.
The inventive devices, which have been described above in an exemplarily manner, can be modified in various ways. In the embodiments according to FIGS. 1, 2, 5 and 7, the adjusting device 40 may, for example, comprise a hydraulic cylinder whose hydraulic fluid is pressurized fuel, e.g., diesel fuel diverted from a common rail system, so that no separate hydraulic pressure source is required. The hydraulic cylinder is controlled in a known manner using valves that are actuated by an electronic control device, dependent on the torque fluctuation compensation required at the respective load point of the internal combustion engine. The described pivoting of the bearing shield 16 can be replaced by a linear movability of the bearing shield in a coulisse that is affixed to the crankcase. The invention is suited for use in reciprocating-piston internal combustion engines as well as in rotary-piston internal combustion engines.
Instead of, or in addition to, the adjustability of the bearing shield 16, the compensating mass element 14 can be formed such that its moment of inertia 14 is changeable, e.g., by providing the compensating mass element with two mass bodies whose spacing is changeable. By changing the moment of inertia, the device can be adapted to the respective to-be-compensated rotational non-uniformities.
The inventive device having the compensating mass element and the coupling with the crankshaft may be disposed variously, for example, at an end of the crankshaft or—in engines with plural cylinders—between the pistons. Several inventive devices can be provided on one crankshaft.
REFERENCE NUMBER LIST
10 crankshaft
12 driver extension
14 compensating mass element
16 bearing shield
20 through-hole
22 guide coupler
24 radial arm
26 connecting member
28 connecting member
29 hinge
40 adjusting device
42 actuator
44 arm
46 arm
48 stop
50 stop
52 connecting member
54 arm
56 arm
58 connecting member
60 piston
62 piston rod
64 circumferential toothing
66 compensating mass element
68 circumferential toothing
72 piston
74 piston-cylinder unit
74 conduit
76 conduit
80 one-way valve
82 one-way valve
84 shutoff valve
86 shutoff valve
88 compensating mass element
90 unbalanced mass
92 unbalanced mass
Patent Application
20110083631
